Patent Publication Number: US-10764503-B2

Title: Information processing apparatus, control method, and program for outputting a guide for correcting a field of view of a camera

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
     This application is a Continuation of U.S. application Ser. No. 16/065,530 filed Jun. 22, 2018 which is a National Stage of International Application No. PCT/JP2016/084406 filed Nov. 21, 2016, claiming priority based on Japanese Application No. 2015-255924 filed Dec. 28, 2015, the contents of which are incorporated herein by reference in their entirety. 
    
    
     TECHNICAL FIELD 
     The present invention relates to an information processing apparatus, a control method, and a program. 
     BACKGROUND ART 
     A body-worn camera that is mounted on, for example, the shoulder of a person has been used. For example, a security guard stands guard while wearing the body-worn camera. Therefore, the guard can remotely monitor a video captured by the body-worn camera or can analyze the video while standing guard in a spot. 
     A technique for making it easy to use a body-worn camera has been developed. For example, Patent Document 1 discloses a technique that easily adjusts the position of a glasses-type head-mounted display. The head-mounted display disclosed in Patent Document 1 is fixed to the head of the user by a fixing portion that presses both regions of the head of the user with appropriate force and an arm that extends from the frontal region of the head to the top of the head. A display corresponding to a lens portion of the glasses is connected to the arm by a rotating mechanism unit. The user can use the rotation mechanism unit to move up or down the display in a state in which the fixing portion and the arm are fixed to the head of the user. 
     The head-mounted display disclosed in Patent Document 1 is provided with three cameras. First, two cameras are provided at the sides of the display. In addition, one camera is provided at the top of the head of the arm. 
     As described above, since the display is movable, the display is moved to change the fields of view of the cameras provided in the display. In contrast, since the position of the camera provided at the top of the head is fixed, the field of view of the camera is fixed. Therefore, the head-mounted display disclosed in Patent Document 1 compares an image that is generated by the camera fixed to the top of the head with an image that is generated by the camera provided in the display to determine whether the display is located at a predetermined position. 
     RELATED DOCUMENT 
     Patent Document 
     
         
         [Patent Document 1] Japanese Patent Application Publication No. 2001-211403 
       
    
     SUMMARY OF THE INVENTION 
     Technical Problem 
     In some cases, for example, a guard wears a head-mounted display and has a separate camera mounted on the shoulder or the chest. For example, a camera provided in the head-mounted display is used to capture a scene in a wide range and the camera mounted on the shoulder is used to capture a close-up image of the face of a person. 
     Here, in a case in which the field of view of the camera mounted on, for example, the shoulder is not correct, the incorrect angle of view causes problems in monitoring or analyzing images. The premise of the technique disclosed in Patent Document 1 is that both the camera that is a reference for adjusting a position and the camera the position of which is to be adjusted are provided in the head-mounted display. Therefore, in the technique disclosed in Patent Document 1, it is difficult to determine whether the field of view of the camera mounted on, for example, the shoulder is correct. 
     The invention has been made in view of the above-mentioned problems. An object of the invention is to provide a technique that can recognize the shift of the field of view of a camera mounted on the body of a person. 
     Solution to Problem 
     An information processing apparatus according to the invention includes: 1) a determination unit that determines whether a field of view of a second camera worn by a person is correct, on the basis of a first captured image which is generated by a first camera worn by the person, a second captured image generated by the second camera, and relationship information indicating a predetermined relationship to be satisfied between a field of view of the first camera and the field of view of the second camera; and 2) a notification unit that, in a case in which the field of view of the second camera is determined to be incorrect, notifies that the field of view of the second camera is not correct. The first camera is provided in a head-mounted display worn by the person. The second camera is provided in a part other than the head-mounted display. 
     A control method according to the invention is performed by a computer. The control method includes: 1) a determination step of determining whether a field of view of a second camera worn by a person is correct, on the basis of a first captured image which is generated by a first camera worn by the person, a second captured image generated by the second camera, and relationship information indicating a predetermined relationship to be satisfied between a field of view of the first camera and the field of view of the second camera; and 2) a notification step of, in a case in which the field of view of the second camera is determined to be incorrect, notifying that the field of view of the second camera is not correct. The first camera is provided in a head-mounted display worn by the person. The second camera is provided in a part other than the head-mounted display. 
     A program according to the invention causes a computer to perform each step of the control method according to the invention and causes the computer to operate as the information processing apparatus according to the invention. 
     Advantageous Effects of Invention 
     The invention provides a technique that can recognize the shift of the field of view of a camera mounted on the body of a person. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The above-mentioned object, other objects, features, and advantages of the invention will become apparent from the following preferred example embodiments and the following accompanying drawings. 
         FIG. 1  is a conceptual diagram illustrating the operation of an information processing apparatus according to Example Embodiment 1. 
         FIG. 2  is a block diagram illustrating the information processing apparatus according to Example Embodiment 1. 
         FIG. 3  is a diagram illustrating the configuration of a computer that implements the information processing apparatus. 
         FIG. 4  is a flowchart illustrating the flow of a process performed by the information processing apparatus according to Example Embodiment 1. 
         FIG. 5  is a first conceptual diagram illustrating relationship information. 
         FIG. 6  is a second conceptual diagram illustrating relationship information. 
         FIG. 7  is a diagram illustrating a case in which a portion in which the head of a person is assumed to be included is determined as a predetermined range. 
         FIG. 8  is a conceptual diagram illustrating a determination method in Case 2. 
         FIGS. 9A-9C  are conceptual diagrams illustrating a determination method in Case 3. 
         FIG. 10  is a diagram illustrating notification information displayed on a display device. 
         FIG. 11  is a block diagram illustrating an information processing apparatus according to Example Embodiment 2. 
         FIG. 12  is a flowchart illustrating the flow of a process performed by the information processing apparatus according to Example Embodiment 2. 
         FIGS. 13A-13C  are diagrams illustrating a guide displayed on the display device. 
         FIGS. 14A-14B  are diagrams illustrating a scene in which a predetermined region or a predetermined range is displayed as a portion of the guide on the display device. 
         FIG. 15  is a diagram illustrating a case in which a first camera is provided in a part other than the head-mounted display. 
     
    
    
     DESCRIPTION OF EMBODIMENTS 
     Hereinafter, example embodiments of the invention will be described with reference to the drawings. However, in all of the drawings, the same components are denoted by the same reference numerals and the description thereof will not be repeated. In addition, in each block diagram except a diagram illustrating a hardware configuration, each block does not indicate a hardware unit, but indicates a functional unit. 
     Example Embodiment 1 
       FIG. 1  is a conceptual diagram illustrating the operation of an information processing apparatus  2000  according to Example Embodiment 1. A user  30  wears a head-mounted display  10 . The user  30  is, for example, a security guard that guards an event site. The head-mounted display  10  includes a first camera  12  and a display device  14 . The first camera  12  is a camera that captures an image of the surroundings. The display device  14  displays an arbitrary image. Since the head-mounted display  10  displays an arbitrary image on the display device  14 , the user can see a scene in which the arbitrary image is superimposed on surrounding scenery. For example, the head-mounted display  10  recognizes the surrounding scenery on the basis of a captured image generated by the first camera  12  and displays an augmented reality (AR) image on the display device  14  according to the surrounding scenery. 
     The user  30  also wears a second camera  20 . The second camera  20  is a camera that captures an image of the surroundings and is mounted at an arbitrary position other than the head-mounted display  10 . For example, the second camera  20  is a surveillance camera that generates a surveillance image for monitoring the surroundings of the user  30 . 
     The information processing apparatus  2000  determines whether the field of view of the second camera  20  is correct. The information processing apparatus  2000  uses a first captured image  40  generated by the first camera  12  and a second captured image  50  generated by the second camera  20  for the determination. Here, the user  30  has two cameras, such as the first camera  12  and the second camera  20 , mounted on the body. Therefore, for example, calibration is performed in advance to determine the relationship to be satisfied between the field of view of the first camera  12  and the field of view of the second camera  20 . The information processing apparatus  2000  compares the first captured image  40  with the second captured image  50  to determine whether the relationship to be satisfied between the field of view of the first camera  12  and the field of view of the second camera  20  is satisfied. In a case in which the relationship is not satisfied, the information processing apparatus  2000  determines that the field of view of the second camera  20  is not correct. 
     Then, in a case in which the field of view of the second camera  20  is not correct, the information processing apparatus  2000  notifies that the field of view of the second camera  20  is not correct. The notification method may be an arbitrary method that is perceivable by the user  30 . 
     In order to achieve the above-mentioned function, the information processing apparatus  2000  includes a determination unit  2020  and a notification unit  2040 .  FIG. 2  is a block diagram illustrating the information processing apparatus  2000  according to Example Embodiment 1. The determination unit  2020  determines whether the field of view of the second camera  20  is correct on the basis of the first captured image  40 , the second captured image  50 , and relationship information. The relationship information is information indicating the relationship to be satisfied between the field of view of the first camera  12  and the field of view of the second camera  20 . In a case in which the field of view of the second camera  20  is not correct, the notification unit  2040  notifies that the field of view of the second camera  20  is not correct. 
     Advantageous Effect 
     The information processing apparatus  2000  according to this example embodiment determines whether the field of view of the second camera  20  is correct, on the basis of the first captured image  40  generated by the first camera  12  that is provided in the head-mounted display and the second captured image  50  generated by the second camera  20  that is mounted on a part of the user  30  other than the head-mounted display  10 , and the relationship information indicating the relationship to be satisfied between the field of view of the first camera  12  and the field of view of the second camera  20 . Then, the information processing apparatus  2000  notifies that the field of view of the second camera  20  is not correct. 
     According to this configuration, it is possible to determine whether the field of view of the second camera  20  provided in a part other than the head-mounted display  10  is correct. Therefore, the user  30  can recognize the shift of the field of view of the second camera  20  provided in a part other than the head-mounted display  10 . As a result, it is possible to easily correct the field of view of the second camera  20 . 
     Next, the information processing apparatus  2000  according to this example embodiment will be described in more detail. 
     Example of Hardware Configuration of Information Processing Apparatus  2000   
     Each functional unit of the information processing apparatus  2000  may be implemented by hardware (for example, a hard-wired electronic circuit) that implements each function unit or a combination of hardware and software (for example, a combination of an electronic circuit and a program controlling the electronic circuit). Hereinafter, a case in which each functional unit of the information processing apparatus  2000  is implemented by a combination of hardware and software will be further described. 
       FIG. 3  is a diagram illustrating the configuration of a computer  1000  that implements the information processing apparatus  2000 . The computer  1000  is various types of computers, such as a personal computer (PC), a server apparatus, and a portable terminal. For example, the computer  1000  is provided as the head-mounted display  10 . In addition, for example, the computer  1000  may be provided as the second camera  20 . 
     The computer  1000  includes a bus  1020 , a processor  1040 , a memory  1060 , a storage  1080 , an input/output interface  1100 , and a network interface  1120 . The bus  1020  is a data transmission path through which the processor  1040 , the memory  1060 , the storage  1080 , the input/output interface  1100 , and the network interface  1120  transmit and receive data. However, a method for connecting, for example, the processor  1040  is not limited to bus connection. The processor  1040  is a processor such as a central processing unit (CPU) or a graphics processing unit (GPU). The memory  1060  is, for example, a random access memory (RAM) or a read only memory (ROM). The storage  1080  is a storage device such as a hard disk, a solid state drive (SSD), or a memory card. The storage  1080  may be a memory such as a RAM or a ROM. 
     The input/output interface  1100  is an interface for connecting the computer  1000  and an input/output device. For example, in a case in which the computer  1000  is provided as the head-mounted display  10 , the first camera  12  or the display device  14  is connected to the input/output interface  1100 . 
     The network interface  1120  is an interface for connecting the computer  1000  to a network. For example, in a case in which the computer  1000  is provided as the head-mounted display  10 , the second camera  20  is connected to the network interface  1120 . The computer  1000  acquires the second captured image  50  generated by the second camera  20  through the network. 
     The storage  1080  stores program modules that implement each function of the information processing apparatus  2000 . The processor  1040  executes each program module to implement each function corresponding to the program modules. Here, in a case in which the processor  1040  executes each module, the processor  1040  may read the modules to the memory  1060  and execute the modules, or may execute the modules, without reading the modules to the memory  1060 . 
     The hardware configuration of the computer  1000  is not limited to the configuration illustrated in  FIG. 3 . For example, each program module may be stored in the memory  1060 . In this case, the computer  1000  may not include the storage  1080 . In addition, for example, the second camera  20  may not be connected to the computer  1000  through the input/output interface  1100 , but may be connected to the computer  1000  through the network interface  1120 . 
     &lt;&lt;As to First Camera  12 &gt;&gt; 
     The first camera  12  is a camera that is provided at an arbitrary position of the head-mounted display  10 . The first camera  12  may be any camera that can capture an image of the surroundings of the head-mounted display  10 . The first camera  12  repeatedly performs an imaging process and generates the first captured image  40  indicating the result of each imaging process. 
     &lt;&lt;As to Second Camera  20 &gt;&gt; 
     The second camera  20  is a camera that is fixed to an arbitrary position (for example, the shoulder or the chest) of the user  30 . The second camera  20  may be any camera that can capture an image of the surroundings of the second camera  20 . For example, second camera  20  is a surveillance video camera. The second camera  20  repeatedly performs an imaging process and generates the second captured image  50  indicating each imaging result. 
     As described above, the computer  1000  may be implemented as the second camera  20 . In this case, the second camera  20  compares the second captured image  50  generated by the second camera  20  with the first captured image  40  generated by the first camera  12  to determine whether the relationship to be satisfied between the field of view of the first camera  12  and the field of view of the second camera  20  is satisfied (the determination unit  2020 ). In a case in which the relationship is not satisfied, the second camera  20  notifies that the field of view of the second camera  20  is not correct (the notification unit  2040 ). 
     The second camera  20  that gives the functions of the information processing apparatus  2000  in this way may be a camera, such as an intelligent camera, a network camera, or an Internet protocol (IP) camera. 
     &lt;Flow of Process&gt; 
       FIG. 4  is a flowchart illustrating the flow of a process performed by the information processing apparatus  2000  according to Example Embodiment 1. The determination unit  2020  acquires the first captured image  40  and the second captured image  50  (S 102 ). The determination unit  2020  acquires the relationship information (S 104 ). The determination unit  2020  determines whether the field of view of the second camera  20  is correct on the basis of the first captured image  40 , the second captured image  50 , and the relationship information (S 106 ). In a case in which the field of view of the second camera  20  is correct (S 106 : YES), the process illustrated in  FIG. 4  ends. On the other hand, in a case in which the field of view of the second camera  20  is not correct (S 106 : NO), the process illustrated in  FIG. 4  proceeds to S 108 . In S 108 , the notification unit  2040  performs notification (S 110 ). 
     &lt;Method for Acquiring First Captured Image  40 &gt; 
     The information processing apparatus  2000  acquires the first captured image  40  (S 102 ). The information processing apparatus  2000  acquires the first captured image  40  using various methods. For example, the information processing apparatus  2000  acquires the first captured image  40  from the first camera  12 . In this case, the information processing apparatus  2000  and the first camera  12  are connected such that they can communicate with each other. 
     In a case in which the first camera  12  stores the captured image in an external storage device, the information processing apparatus  2000  acquires the first captured image  40  from the storage device. In this case, the information processing apparatus  2000  and the storage device are connected such that they can communicate with each other. 
     The timing when the information processing apparatus  2000  acquires the first captured image  40  is not particularly limited. For example, the information processing apparatus  2000  acquires the generated first captured image  40  at the timing when the first captured image  40  is generated. In addition, for example, the information processing apparatus  2000  may periodically acquire the first captured image  40 . In the latter case, the information processing apparatus  2000  may collectively acquire a plurality of first captured images  40 . 
     &lt;Method for Acquiring Second Captured Image  50 &gt; 
     The method used by the information processing apparatus  2000  to acquire the second captured image  50  and the timing when the information processing apparatus  2000  acquires the second captured image  50  are the same as the method used by the information processing apparatus  2000  to acquire the first captured image  40  and the timing when the information processing apparatus  2000  acquires the first captured image  40 , respectively. 
     Note that, in a case in which the information processing apparatus  2000  is implemented as the second camera  20 , the information processing apparatus  2000  acquires the second captured image  50  generated by the information processing apparatus  2000 . In this case, the second captured image  50  is stored in, for example, the memory  1060  or the storage  1080  (see  FIG. 3 ) provided in the information processing apparatus  2000 . 
     &lt;Details of Relationship Information&gt; 
     The relationship information indicates the relationship to be satisfied between the field of view of the first camera  12  and the field of view of the second camera  20 . Hereinafter, the relationship information will be described in detail. 
     &lt;&lt;Relationship Information 1&gt;&gt; 
     For example, the relationship to be satisfied between the field of view of the first camera  12  and the field of view of the second camera  20  is the relationship in which “the field of view of the second camera  20  includes a predetermined range of the field of view of the first camera  12 ”. In this case, the relationship information includes information for specifying the predetermined range. 
       FIG. 5  is a first conceptual diagram illustrating the relationship information. In  FIG. 5 , a field of view  90  indicates the field of view of the first camera  12 . A predetermined range  100  indicates a range in the field of view of the first camera  12 , the range having to be included in the field of view of the second camera  20 . For example, the relationship information specifies the predetermined range  100  with “the coordinates of an upper end, a width, and a height”. In  FIG. 5 , the coordinates of the upper end, width, and height of the predetermined range  100  are (x1, y1), w1, and h1, respectively. Here, in the coordinate system illustrated in  FIG. 5 , the origin is the upper left end of the field of view  90 , the X direction is the right direction, and the Y direction is the downward direction. In addition, both the width and height of the predetermined range  100  are relative lengths in a case in which the width and height of the field of view  90  are 1. 
     Note that, for convenience, in the relationship information illustrated in  FIG. 5 , the size of the predetermined range  100  is represented by an absolute value. However, the value indicating the relationship information is not limited to the absolute value. For example, the relationship information may be configured such that the size of the predetermined range  100  is represented by the number of pixels. In addition, the X direction and the Y direction are not limited to the directions illustrated in  FIG. 5 . Any coordinate system can be used as long as it can describe the directions. However, in the following description, the same coordinate system as that illustrated in  FIG. 5  is used. 
     The predetermined range  100  indicated by the relationship information may be fixedly set in advance or may be dynamically set. In the latter case, the predetermined range  100  may be manually set or may be set by an arbitrary computer (for example, the information processing apparatus  2000 ). 
     For example, the computer changes the position of the predetermined range  100  depending on the orientation of the face of the user  30 . In a case in which the orientation of the face of the user  30  changes, the scenery in the first captured image  40  changes. In general, it is preferable to fixedly set the predetermined range  100  with respect to a specific region (for example, a region through which a person passes frequently) of the scenery in the first captured image  40  rather than to fixedly set the predetermined range  100  at a predetermined position on the first captured image  40 . Therefore, the computer sets the position of the predetermined range  100  according to a change in the orientation of the face of the user  30 . 
     For example, the computer performs matching between a plurality of first captured images  40  (frames forming a video generated by the first camera  12 ) to detect the movement of the entire scenery in the first captured image  40 . Then, the computer shifts the position of the predetermined range  100  in a direction in which the movement is offset. For example, in a case in which it is detected that the entire scenery in the first captured image  40  has been moved by (dx, dy), the computer shifts the position of four corners of the predetermined range  100  from the current position by (−dx, −dy). 
     Here, as a method for performing the matching between the frames, various methods can be used. For example, the following methods can be used: a method that simply calculates an optical flow; and a method that extracts feature points and performs matching between the feature points. 
     &lt;&lt;Relationship Information 2&gt;&gt; 
     For example, the relationship to be satisfied between the field of view of the first camera  12  and the field of view of the second camera  20  is the relationship in which “the field of view of the second camera  20  includes a predetermined range of the field of view of the first camera  12  in the vertical direction or the horizontal direction of the field of view of the first camera  12 ”. In this case, the relationship information includes information for specifying the predetermined range. 
       FIG. 6  is a second conceptual diagram illustrating the relationship information. A field of view  120  indicates the field of view of the second camera  20 . A predetermined range  110  indicates a range in the vertical direction of the field of view  90  of the first camera  12 , the rage having to be included in the field of view  120  of the second camera  20 . The conditions to be satisfied by the field of view  120  in the vertical direction are that the Y coordinate of the upper end of the field of view  120  is equal to or less than y1 and the Y coordinate of the lower end of the field of view  120  is equal to or greater than y2. In addition, the condition to be satisfied by the field of view  120  in the horizontal direction is that the field of view  120  is included in the field of view  90  of the first camera  12 . In other words, the position of the field of view  120  in the horizontal direction may be any position included in the field of view  90 . 
     In  FIG. 6 , four fields of view  120  of the second camera  20  are illustrated. All of a field of view  120 - 1 , a field of view  120 - 2 , and a field of view  120 - 3  satisfy the above-mentioned conditions. Therefore, in a case in which the field of view of the second camera  20  is any one of the fields of view  120 - 1  to  120 - 3 , the determination unit  2020  determines that the field of view of the second camera  20  is correct. On the other hand, a field of view  120 - 4  does not satisfy the conditions in the vertical direction. Therefore, in a case in which the field of view of the second camera  20  is the field of view  120 - 4 , the determination unit  2020  determines that the field of view of the second camera  20  is not correct. 
     For example, it is assumed that, while the first camera  12  is used to capture an image of an entire person, the second camera  20  is used to capture an enlarged image of a predetermined part (for example, the head) of the person. In this case, the field of view  120  of the second camera  20  needs to include a range that is assumed to include the predetermined part in the field of view  90  of the first camera  12 . Therefore, for example, in the relationship information illustrated in  FIG. 6 , the predetermined range  110  indicates the range that is assumed to include the head of the person in the field of view  90  of the first camera  12 . 
       FIG. 7  is a diagram illustrating a case in which a portion that is assumed to include the head of the person is determined as the predetermined range  110 . In  FIG. 7 , the field of view  90  of the first camera  12  includes a scene in which a plurality of persons  130  walk on a street  140 . All of the heads of the persons  130  are included in the predetermined range  110 . Therefore, in a case in which the field of view  120  of the second camera  20  includes the predetermined range  110  in the vertical direction, the second captured image  50  includes the head of the person. 
     Note that, an example of the relationship information illustrated in  FIG. 6  indicates the conditions of the field of view  120  of the second camera  20  in the vertical direction. However, the relationship information may indicate the conditions of the field of view  120  of the second camera  20  in the horizontal direction, using the same method as described above. 
     As described above, in a case in which the second camera  20  is used to capture an enlarged image of a predetermined part of a person, the relationship information may be information indicating the condition in which “in a case in which a person is included in the predetermined range  110  of the first camera  12 , a predetermined part of the person is included in the field of view  120  of the second camera  20 ”. 
     The predetermined range  110  indicated by the relationship information is set by various methods. In a case in which the position where the user  30  stands is fixed, for example, the first captured image  40  generated by the first camera  12  in a state in which the user  30  stands at a predetermined position is acquired in advance, and the first captured image  40  is used to set the predetermined range  110 . The setting may be manually performed or may be performed by an arbitrary computer (for example, the information processing apparatus  2000 ). 
     In a case in which the predetermined range  110  is set by a computer, for example, the computer detects the head of the person included in the first captured image  40 . Alternatively, instead of directly detecting the head, the computer may detect the upper half of the body and may use an upper part of the upper half as the head. Then, the computer sets the predetermined range  110  on the basis of the position of the detected head in the Y-axis direction. 
     For example, it is assumed that the height (y2-y1 in  FIG. 6 ) of the predetermined range  110  is predetermined. In this case, the computer sets, as the predetermined range  110 , a range which has the detected position of the head in the Y-axis direction as the center and has the predetermined height. In addition, for example, in a case in which information about belongings or clothes is desired to be acquired together with the head, the computer may set the predetermined range  110  such that the detected position of the head in the Y-axis direction is slightly above the center (has a value close to y1). In this case, for example, the computer sets the predetermined range  110  such that a point which internally divides an interval between y1 and y2 at a ratio of 1:α (α is a value greater than 1) is the center of the head. 
     For example, it is assumed that the heads of a plurality of persons are detected from the first captured image  40 . In this case, for example, the computer sets the position (hereinafter, referred to as Ymin) of the head whose Y coordinate is the smallest as the upper end of the predetermined range  110 , and sets the position (hereinafter, referred to as Ymax) of the head whose Y coordinate is the largest as the lower end of the predetermined range  110 . Alternatively, the computer may set a margin of a predetermined width Δ and may set a range from Ymin−Δ to Ymax+Δ as the predetermined range  110 . Information indicating the predetermined width Δ may be set in the computer in advance or may be stored in a storage device that can be accessed by the computer. 
     In a case in which the user  30  moves, in some cases, the range (predetermined range  110 ) in which the head of the person is assumed to be included in the field of view  90  of the first camera  12  is changed. In this case, the relationship information indicating the predetermined range  110  may be dynamically updated by an arbitrary computer (for example, the information processing apparatus  2000 ). For example, the computer periodically acquires the first captured image  40  and sets the predetermined range  110  on the basis of the position of the head of the person detected from the first captured image  40  as described above. 
     The dynamic update of the relationship information makes it possible to appropriately use the relationship information according to the movement of the user  30 . Therefore, even in a case in which the user  30  moves, the information processing apparatus  2000  can appropriately determine whether the field of view of the second camera  20  becomes an intended field of view. 
     Note that, the relationship information may be information set in the determination unit  2020  or may be information stored in a storage device that can be accessed by the determination unit  2020 . 
     &lt;Details of Determination Unit  2020 &gt; 
     The determination unit  2020  determines whether the field of view of the second camera  20  is correct on the basis of the first captured image  40 , the second captured image  50 , and the relationship information (S 106 ). Here, the scenery included in the first captured image  40  indicates scenery included in the field of view of the first camera  12 . In contrast, the scenery included in the second captured image  50  indicates scenery included in the field of view of the second camera  20 . The determination unit  2020  determines whether the field of view of the second camera  20  is correct on the basis of the field of view of the first camera  12  indicated by the first captured image  40 , the field of view of the second camera  20  indicated by the second captured image  50 , and the relationship information. 
     A specific method for determining whether the field of view of the second camera  20  is correct depends on what kind of information the relationship information indicates. Next, a specific method for determining whether the field of view of the second camera  20  is correct will be described. 
     &lt;&lt;Case 1&gt;&gt; 
     It is assumed that the relationship information indicates the relationship in which “the field of view of the second camera  20  includes a predetermined range of the field of view of the first camera  12 ” like the above-mentioned Relationship Information 1. In this case, the relationship information includes information for specifying the predetermined range  100  illustrated in  FIG. 5 . 
     The determination unit  2020  determines whether the scenery in the predetermined range  100  of the first captured image  40  is included in the scenery captured by the second camera  20 . In a case in which the scenery in the predetermined range  100  of the first captured image  40  is included in the scenery captured by the second camera  20 , the determination unit  2020  determines that the field of view of the second camera  20  is correct. On the other hand, in a case in which the scenery in the predetermined range  100  of the first captured image  40  is not included in the scenery captured by the second camera  20 , the determination unit  2020  determines that the field of view of the second camera  20  is not correct. 
     Various methods are used to determine whether the scenery in the predetermined range  100  of the first captured image  40  is included in the scenery captured by the second camera  20 . For example, the determination unit  2020  calculates a feature value of the predetermined range  100  of the first captured image  40  and a feature value of the second captured image  50 . The feature value of the image is data indicating, for example, a characteristic color, pattern, or shape included in the image. In addition, the determination unit  2020  calculates the degree of matching between the feature values. For example, the determination unit  2020  calculates feature points of the first captured image  40  and the second captured image  50 , extracts feature values in the vicinity of the feature points, and performs matching between the feature points to calculate the degree of matching between the feature values of the images. 
     In a case in which the matching is performed, when the magnification ratio of the first captured image  40  to the second captured image  50  is known, the determination unit  2020  can perform the matching at a high speed, using information indicating the magnification ratio. For example, it is assumed that the length of a certain object is L1 pixels in the first captured image and is L2 pixels in the second captured image  50 . In this case, the determination unit  2020  performs the matching between the second captured image scaled by L1/L2 and the first captured image. As such, in a case in which the matching is performed considering the magnification ratio, it is possible to perform the matching at a higher speed than that in a case in which the magnification ratio is not considered. 
     In a case in which the degree of matching between the features is equal to or greater than a predetermined value, the determination unit  2020  determines that the scenery in the predetermined range  100  of the first captured image  40  is included in the scenery in the second captured image  50 . In this case, the determination unit  2020  determines that the field of view of the second camera  20  is correct. On the other hand, in a case in which the degree of matching between the features is less than the predetermined value, the determination unit  2020  determines that the scenery in the predetermined range  100  of the first captured image  40  is not included in the scenery in the second captured image  50 . In this case, the determination unit  2020  determines that the field of view of the second camera  20  is not correct. Alternatively, the determination unit  2020  may perform the same determination process as described above for a case in which there exists a region in which the degree of matching between the feature values is equal to or greater than the predetermined value outside the predetermined range  100 . 
     For example, the determination unit  2020  determines whether the scenery in the predetermined range  100  of the first captured image  40  is included in the scenery in the second captured image  50 , on the basis of the degree of matching between the number of persons in the predetermined range  100  of the first captured image  40  and the number of persons in the second captured image  50 . Specifically, first, the determination unit  2020  performs a person detection process for the predetermined range  100  of the first captured image  40  to detect the number of persons in the predetermined range  100 . Similarly, the determination unit  2020  performs the person detection process for the second captured image  50  to detect the number of persons in the second captured image  50 . Then, the determination unit  2020  calculates the degree of matching between the number of persons in the predetermined range  100  of the first captured image  40  and the number of persons in the second captured image  50 . For example, the degree of matching is a value obtained by dividing the number of persons in the predetermined range  100  of the first captured image  40  by the number of persons in the second captured image  50 . 
     In a case in which the degree of matching is equal to or greater than a predetermined value, the determination unit  2020  determines that the scenery in the predetermined range  100  of the first captured image  40  is included in the scenery in the second captured image  50 . In this case, the determination unit  2020  determines that the field of view of the second camera  20  is correct. On the other hand, in a case in which the degree of matching is less than the predetermined value, the determination unit  2020  determines that the scenery in the predetermined range  100  of the first captured image  40  is not included in the scenery in the second captured image  50 . In this case, the determination unit  2020  determines that the field of view of the second camera  20  is not correct. For example, it is required that the scenery in the first captured image  40  and the scenery in the second captured image  50  are matched with each other in a case in which the field of view of the second camera  20  is correct, the predetermined value is set to 1. 
     Note that, the person detection process for the first capture image  40  and that for the second capture image  50  are not necessarily the same as each other. The determination unit  2020  may be configured so as to perform an appropriate person detection process according to, for example, resolution. For example, the determination unit  2020  can use various methods, such as a method for detecting the entire person or a method for detecting only the upper half of the body, according to resolution. 
     As described above, in some cases, the second camera  20  is used to capture an enlarged image of a predetermined part (for example, the head) of the person. In this case, when the number of persons in the second captured image  50  is calculated, the determination unit  2020  may perform a process of detecting a predetermined part of a person for the second captured image  50  and may use the number of detected predetermined parts as the number of persons in the second captured image  50 . For example, in a case in which the predetermined part is the head, the determination unit  2020  performs a head detection process or a face detection process. 
     In this way, the determination unit  2020  determines that the field of view of the second camera  20  is not correct in a case in which the degree of matching between the number of persons in the predetermined range  100  of the first captured image  40  and the number of predetermined parts of the persons in the second captured image  50  is less than a predetermined value. With this configuration, in a case in which a predetermined part of the person is not capable of being correctly captured in the field of view of the second camera  20 , the user  30  can recognize the fact. 
     Note that, the information indicating which part of the person is the predetermined part may be set in the determination unit  2020  in advance or may be stored in a storage device that can be accessed by the determination unit  2020 . 
     Note that, a method for determining whether a predetermined part of the person is included in the second captured image  50  is not limited to the method that performs the detection process of a predetermined part for the second captured image  50 . For example, the determination unit  2020  may perform a process of detecting parts other than a predetermined part for the second captured image  50  and may determine whether the predetermined part is included in the second captured image  50  on the basis of the result of the process. 
     For example, it is assumed that the predetermined part is the head. In this case, when the feet of a person are included in the second captured image  50 , the probability that the head of the person will be included in the second captured image  50  is low. Therefore, the determination unit  2020  performs a process of detecting the feet of a person for the second captured image  50 . In a case in which the feet of the person are detected, the determination unit  2020  determines that the head, which is the predetermined part, is not included in the second captured image  50 . On the other hand, in a case in which the feet of the person are not detected, the determination unit  2020  determines that the head, which is the predetermined part, is included in the second captured image  50 . 
     In addition, the determination unit  2020  may determine whether the field of view of the second camera  20  is correct on the basis of the degree of matching between various objects in the predetermined range  100  of the first captured image  40  and various objects captured by the second camera  20 . The object may or may not include a person. For example, the object is a road sign, a road cone, a tire of a vehicle, or a window frame of a house or a vehicle. 
     Information indicating the type of object may be set in the determination unit  2020  in advance or may be stored in a storage device that can be accessed by the determination unit  2020 . 
     Specifically, the determination unit  2020  performs an object detection process for the predetermined range  100  of the first captured image  40  and the entire second camera  20  to detect objects. Then, the determination unit  2020  calculates the degree of matching between an object in the predetermined range  100  of the first captured image  40  and an object captured by the second camera  20 . For example, the degree of matching is a value indicating the proportion of the number of objects captured by the second camera  20  to the number of objects in the predetermined range  100  of the first captured image  40 . 
     In a case in which the degree of matching is equal to or greater than a predetermined value, the determination unit  2020  determines that the scenery in the predetermined range  100  of the first captured image  40  is included in the scenery in the second captured image  50 . In this case, the determination unit  2020  determines that the field of view of the second camera  20  is correct. On the other hand, in a case in which the degree of matching is less than the predetermined value, the determination unit  2020  determines that the scenery in the predetermined range  100  of the first captured image  40  is not included in the scenery in the second captured image  50 . In this case, the determination unit  2020  determines that the field of view of the second camera  20  is not correct. 
     Alternatively, the determination unit  2020  may also use the positional relationship between the detected objects. For example, in a case in which a road cone detected from a lower portion of the predetermined range  100  in the first captured image  40  is detected from an upper portion of the second captured image  50  or in a case in which a sign detected from an upper portion of the predetermined range  100  in the first captured image  40  is detected from a lower portion of the second captured image  50 , the determination unit  2020  determines that the field of view of the second camera  20  is not correct. 
     Alternatively, the determination unit  2020  may detect an object that is present outside the predetermined range  100  in the first captured image  40  and may determine whether the object outside the predetermined range  100  is included in the second captured image  50 . In a case in which the object outside the predetermined range  100  is included in the second captured image  50 , the determination unit  2020  determines that the field of view of the second camera  20  is not correct. 
     Note that, the timing when the determination unit  2020  determines whether the scenery in the predetermined range  100  of the first captured image  40  is not included in the scenery in the second captured image  50  is not particularly limited. For example, the determination unit  2020  performs the determination whenever the first captured image  40  and the second captured image  50  are acquired. In addition, for example, the determination unit  2020  periodically performs the determination process. Furthermore, for example, the determination unit  2020  may determine whether a person is included in the predetermined range  100  of the first captured image  40  and may determine whether the scenery in the predetermined range  100  of the first captured image  40  is included in the scenery in the second captured image  50  in a case in which a person is included in the predetermined range  100 . Note that, the process of determining whether a person is included in the predetermined range  100  of the first captured image  40  may be performed whenever the first captured image  40  is acquired or periodically. 
     Alternatively, after determining whether the scenery in the predetermined range  100  of the first captured image  40  is included in the scenery in the second captured image  50  once, the determination unit  2020  may simplify the determination process. For example, after performing the determination process once, the determination unit  2020  may detect the amount of change in the scenery included in the first captured image  40  and may perform the determination process again in a case in which the amount of change is large. 
     The determination unit  2020  determines whether the amount of change in the scenery included in the first captured image  40  is large, using various methods. For example, the determination unit  2020  performs the determination process using an optical flow indicating the movement of the entire first captured image  40 . Specifically, first, the determination unit  2020  calculates the optical flow. Then, in a case in which the average value of the optical flow is greater than a threshold value, the determination unit  2020  determines that the amount of change in the scenery included in the first captured image  40  is large. 
     For example, the determination unit  2020  may generate low-resolution images for each of a plurality of first captured images  40  and may perform the determination process using the low-resolution images. Specifically, the determination unit  2020  calculates a difference between the low-resolution images and determines that the amount of change in the scenery included in the first captured image  40  is large in a case in which the difference is equal to or greater than a predetermined value. 
     For example, the determination unit  2020  may extract background regions of each of a plurality of first captured images  40  and may determine that the amount of change in the scenery included in the first captured image  40  is large in a case in which the difference between the background regions is large. Here, the background region of the first captured image  40  is a region in which a person, which becomes a foreground region, is less likely included. A known technique can be used as a method for extracting the background region from the image. 
     For example, the determination unit  2020  may perform a compression process for a video (a video generated by the first camera  12 ) formed by a plurality of first captured images  40  and may determine that the amount of change in the scenery included in the first captured image  40  is large on the basis of the data size of the compressed video. In general, in a case in which a video is compressed, as the difference between frames increases, the data size of the compressed video increases. For this reason, for example, the determination unit  2020  divides the video generated by the first camera  12  into partial videos at a predetermined time interval and performs the compression process for each partial video. Then, the determination unit  2020  compares the data sizes of the partial videos. Then, in a case in which the difference between the data sizes of the partial videos is large, the determination unit  2020  determines that the amount of change in the scenery included in the first captured image  40  is large. Note that, various known compression methods can be used as the video compression process. 
     Note that, the determination unit  2020  may be configured to perform the determination multiple times and perform a final determination by integrating those results, instead of determining that the field of view of the second camera  20  is not correct based on a single determination alone. In some cases, when the user  30  temporarily changes the orientation of the face to look away, only the scenery in the first captured image  40  is greatly changed and the scenery in the second captured image  50  is little changed. In a case in which the user  30  only temporarily changes the orientation of the face, the user  30  eventually faces the same direction. Therefore, the scenery of the first captured image  40  eventually returns to the original position. In this case, it is considered that the field of view of the second camera  20  is correct. For this reason, the determination unit  2020  performs a plurality of determination processes and integrates the obtained results as described above. Therefore, for example, in a case in which the user  30  temporarily changes the orientation of the face, it is possible to prevent the field of view of the second camera  20  from being instantaneously determined to be incorrect. 
     Note that, the determination unit  2020  may be configured such that it performs the determination process using a combination of the above-mentioned various determination methods. 
     &lt;Case 2&gt; 
     It is assumed that the relationship information indicates the relationship in which “the field of view of the second camera  20  includes a predetermined range of the field of view of the first camera  12  in the vertical direction or the horizontal direction of the field of view of the first camera  12 ”, like the above-mentioned Relationship Information 2. In this case, the relationship information indicates information for specifying the predetermined range  110  illustrated in  FIG. 6 . In the example described with reference to  FIG. 6 , the field of view of the second camera  20  is a correct field of view as long as it includes the predetermined range  110  in the vertical direction. 
     For example, the determination unit  2020  determines whether the predetermined range  110  includes a region indicating the same scenery as that in the second captured image  50 . An example of the comparison method will be described with reference to  FIG. 8 .  FIG. 8  is a conceptual diagram illustrating a determination method according to Case 2. First, the determination unit  2020  extracts comparative region  1  from the first captured image  40 . The comparative region  1  is defined as follows: 1) the comparative region  1  has the same size as the second captured image  50  or has a size that is a predetermined percentage less than the size of the second captured image  50 ; 2) the position of the left end of the comparative region  1  is aligned with the position of the left end of the first captured image  40 ; and 3) the position of the center of the comparative region  1  in the vertical direction is aligned with the position of the center of the predetermined range  110  in the vertical direction. 
     The determination unit  2020  compares scenery in the comparative region  1  of the first captured image  40  with the scenery in the second captured image  50 . In a case in which the scenery in the comparative region  1  of the first captured image  40  is included in the scenery in the second captured image  50 , the determination unit  2020  determines that the field of view of the second captured image  50  is correct. On the other hand, in a case in which the scenery in the comparative region  1  of the first captured image  40  is not included in the scenery in the second captured image  50 , the determination unit  2020  extracts comparative region  2  which is the next comparison target from the first captured image  40 . The comparative region  2  is obtained by shifting the comparative region  1  to the right by “s”. Here, “s” is a predetermined sliding step. Then, the determination unit  2020  performs the same comparison process as that used for the comparative region  1  for the comparative region  2 . 
     The determination unit  2020  repeats the above-mentioned comparison process while shifting the comparative region by “s” until the comparative region including the scenery in the second captured image  50  is found or until the comparative region reaches the right end of the first captured image  40 . In a case in which the comparative region including the scenery in the second captured image  50  is not found even though the comparative region reaches the right end of the first captured image  40 , the determination unit  2020  determines that the field of view of the second camera  20  is not correct. 
     Here, any of various methods described in Case 1 which determine whether the scenery in the predetermined range  100  of the first captured image  40  is included in the scenery in the second captured image  50  can be used as the method which determines whether the scenery in the comparative region of the first captured image  40  is included in the scenery in the second captured image  50 . 
     Note that, the determination unit  2020  may determine the initial position (the left end in  FIG. 8 ) of a comparative region compared with the second captured image  50  and a comparison order (from the left to the right in  FIG. 8 ) on the basis of the results of the determination processes performed in the past (for example, the previous determination process). For example, the determination unit  2020  stores the position of the comparative region specified by the previous determination process and uses the position as the initial position of the comparative region. Then, the determination unit  2020  sequentially compares comparative regions, which are obtained by shifting the comparative region from the initial position to the left and the right by “s”, with the second captured image  50 . It is considered that the probability that scenery in the comparative region which has been matched in the previous process or a neighboring comparative region will be matched with the scenery in the second captured image  50  again is high. For this reason, in a case in which the initial position of the comparative region and the comparison order are determined on the basis of the result of the previous determination process, it is possible to increase the processing speed of the determination unit  2020 . 
     In addition, in a case in which a whole movement of both the first captured image  40  and the second captured image  50  from the time when the previous determination process is performed is obtained, the determination unit  2020  may compensate for the movement and perform the same determination process as described above. For example, it is assumed that a comparative region including the same scenery as that in the second captured image  50  in the previous determination process is located at the position of x1 from the left end of the first captured image  40 . It is assumed that the first captured image  40  to be subjected to the current determination process is shifted by “d”, as compared to the first captured image  40  subjected to the previous determination process. In this case, the determination unit  2020  sets the initial position of the current comparative region to x1-d. 
     Note that, information indicating the sliding step s may be stored in the determination unit  2020  in advance or may be stored in a storage device that can be accessed by the determination unit  2020 . 
     Note that, the timing when the determination unit  2020  performs the process of comparing the comparative region with the second captured image  50  is not particularly limited. For example, the determination unit  2020  performs the determination process whenever the first captured image  40  and the second captured image  50  are acquired. For example, the determination unit  2020  periodically performs the determination process. Note that, for example, the determination unit  2020  may determine whether a person is included in the predetermined range  110  of the first captured image  40  and may perform the comparison process in a case in which a person is included in the predetermined range  110 . In addition, the process of determining whether a person is included in the predetermined range  110  of the first captured image  40  may be performed whenever the first captured image  40  is acquired or may be periodically performed. Alternatively, as described in Case 1, the movement of the entire screen may be detected and the determination process may be performed. 
     For example, in a case in which the road  140  illustrated in  FIG. 7  is guarded, the field of view of the second camera  20  preferably includes the head of the person. Therefore, even in a case in which the field of view of the second camera  20  is changed from the original field of view in the horizontal direction, the change does not affect guarding. In addition, since the security guard stands guard while looking left and right, it is preferable that a change in the field of view of the second camera  20  for the horizontal direction is allowed. 
     According to the determination method in Case 2, in a case in which the field of view of the second camera  20  is changed from the original position in the horizontal direction, but is not changed in the vertical direction, the field of view of the second camera  20  is determined to be correct. Therefore, a change in the field of view of the second camera  20  can be allowed in the range in which, for example, guarding is not affected. As a result, the convenience of the second camera  20  is improved. 
     &lt;&lt;Case 3&gt;&gt; 
     It is assumed that the relationship information indicates the condition in which “in a case in which a person is included in a predetermined range of the field of view of the first camera  12 , a predetermined part of the person is included in the field of view of the second camera  20 ”. In this case, the relationship information includes information for specifying the predetermined range  110  illustrated in  FIG. 6 . In a case in which a person is included in the predetermined range  110  of the first captured image  40  and a predetermined part of the person is included in the second captured image  50 , the determination unit  2020  determines that the field of view of the second camera  20  is not correct. 
     First, the determination unit  2020  performs an object analysis process for the predetermined range  110  of the first captured image  40  to determine whether a person is included in the predetermined range  110 . In a case in which a person is included in the predetermined range  110 , the determination unit  2020  detects a predetermined part of the person from the second captured image  50 . In a case in which a predetermined part of the person is included in the second captured image  50 , the determination unit  2020  determines that the field of view of the second camera  20  is correct. On the other hand, in a case in which a predetermined part of the person is not included in the second captured image  50 , the determination unit  2020  determines that the field of view of the second camera  20  is not correct. 
       FIGS. 9A-9C  are conceptual diagrams illustrating a determination method in Case 3. In this example, the predetermined part of the person is the head.  FIG. 9A  illustrates the first captured image  40 . In  FIG. 9A , the predetermined range  110  includes a person. The determination unit  2020  that has acquired the first captured image  40  determines whether the head of the person is included in the second captured image  50 . In  FIG. 9B , the second captured image  50  includes the head of the person. Therefore, the determination unit  2020  that has acquired the second captured image  50  determines that the field of view of the second camera  20  is correct. In contrast, in  FIG. 9C , the second captured image  50  does not include the head of the person. Therefore, the determination unit  2020  that has acquired the second captured image  50  determines that the field of view of the second camera  20  is not correct. 
     Note that, as described above, the determination of whether a predetermined part of a person is included in the second captured image  50  may be performed on the basis of the result of the process of determining whether parts other than the predetermined part are included in the second captured image  50 . Alternatively, the determination unit  2020  may be configured such that it recognizes an object in the background and performs the determination process. For example, in a case in which, for example, a road cone or a tire of a vehicle (particularly, in an upper region of the second captured image  50 ) is detected, the probability that the head of the person will be included in the second captured image  50  is low. Therefore, for example, in a case in which the predetermined part is the head and a predetermined object, such as a road cone, is included in the second captured image  50 , the determination unit  2020  may determine that the field of view of the second camera  20  is not correct. 
     The timing when the determination unit  2020  performs the process described in Case 3 is not particularly limited. For example, the determination unit  2020  performs the process whenever the first captured image  40  and the second captured image  50  are acquired. In addition, for example, the determination unit  2020  periodically performs the process. The determination unit  2020  may be configured so as to perform the determination process, using a combination of the above-mentioned various determination methods. 
     According to the determination method in Case 3, similarly to the determination method in Case 2, a change in the field of view of the second camera  20  can be allowed in the range in which, for example, guarding is not affected. As a result, the convenience of the second camera  20  is improved. 
     &lt;Details of Notification Unit  2040 &gt; 
     The notification unit  2040  notifies the user  30  that the field of view of the second camera  20  is not correct (S 110 ). Here, information notified to the user  30  is referred to as notification information. The notification information is data of an arbitrary format, such as text data, image data, or voice data. The notification unit  2040  displays the notification information or outputs the notification information as a voice. Then, the user  30  can recognize that the field of view of the second camera  20  is not correct. 
     For example, the notification unit  2040  displays the notification information indicating that the field of view of the second camera  20  is not correct on the display device  14  of the head-mounted display  10 .  FIG. 10  is a diagram illustrating the notification information displayed on the display device  14 . In  FIG. 10 , notification information  150  is displayed on the display device  14 . The user  30  that wears the head-mounted display  10  can see the notification information  150  to recognize that the field of view of the second camera  20  is not correct. 
     Example Embodiment 2 
       FIG. 11  is a block diagram illustrating an information processing apparatus  2000  according to Example Embodiment 2. The information processing apparatus  2000  according to Example Embodiment 2 has the same functions as the information processing apparatus  2000  according to Example Embodiment 1 except the following. 
     The information processing apparatus  2000  according to Example Embodiment 2 includes a guide output unit  2060 . The guide output unit  2060  outputs a guide used to correct the field of view of the second camera  20 . 
     &lt;Flow of Process&gt; 
       FIG. 12  is a flowchart illustrating the flow of a process performed by the information processing apparatus  2000  according to Example Embodiment 2. The information processing apparatus  2000  according to Example Embodiment 2 performs the process from S 102  to S 108  illustrated in  FIG. 4  and then performs S 202 . Some of the steps illustrated in  FIG. 4  are omitted in  FIG. 12  for simplicity of illustration. 
     In S 202 , the guide output unit  2060  outputs the guide for correcting the field of view of the second camera  20  to be correct. 
     &lt;Details of Guide Output Unit  2060 &gt; 
     The guide output from the guide output unit  2060  is arbitrary information that can be used to make the field of view of the second camera  20  correct. The guide is data of an arbitrary format, such as text data, image data, or voice data. The guide output unit  2060  displays the guide on the display or outputs the guide as a voice. The user  30  can adjust the position or the angle of view of the second camera  20  or can correct the field of view of the second camera  20  according to the guide. 
     For example, the guide output unit  2060  displays the guide for correcting the field of view of the second camera  20  on the display device  14  of the head-mounted display  10 .  FIGS. 13A-13C  are diagrams illustrating the guide displayed on the display device  14 . 
     Example 1 of Guide 
     A guide  160 - 1  illustrated in  FIG. 13A  indicates the direction in which the second camera is to be oriented. The user  30  that sees the guide  160 - 1  changes the attachment position of the second camera  20  or changes the angle of view of the second camera  20  to correct the field of view of the second camera  20  until the guide  160 - 1  is not displayed. In this way, the user  30  can correct the field of view of the second camera  20  to a correct field of view. 
     Next, a method for calculating the direction in which the second camera  20  is to be oriented will be described. It is assumed that the relationship information indicates the predetermined range  110  in the field of view of the first camera  12  to be matched with the field of view of the second camera  20  as illustrated in  FIG. 5 . In this case, for example, the guide output unit  2060  calculates the direction which starts from the center of a region of the first captured image  40  matched with the scenery in the second captured image  50  and ends at the center of the predetermined range  100 . Then, the guide output unit  2060  displays an image of an arrow indicating the direction at an arbitrary position on the display device  14 . 
     It is assumed that the relationship information indicates the predetermined range  110  indicating the condition of the field of view of the second camera  20  for the vertical direction as illustrated in  FIG. 6 . In this case, when the region of the first captured image  40  matched with the scenery in the second captured image  50  is located below the predetermined range  110 , the guide output unit  2060  sets the direction in which the second camera  20  is to be oriented to an upward direction. In contrast, when the region of the first captured image  40  matched with the scenery in the second captured image  50  is located above the predetermined range  110 , the guide output unit  2060  sets the direction in which the second camera  20  is to be oriented to a downward direction. 
     Note that, the direction in which the field of view of the second camera  20  is to be oriented may be calculated on the basis of a value measured by a sensor that detects an inclination, such as a gyro sensor. In this case, the information processing apparatus  2000  periodically measures the inclination of the second camera  20 , using the sensor, and stores the measurement results in the storage device. Then, the guide output unit  2060  calculates a difference between the inclination of the second camera  20  when the field of view is correct and the current inclination of the second camera  20  by using the inclination of the second camera  20  which has been measured at each point of time for the period from the time when the field of view of the second camera  20  is correct (for example, the time when the second camera  20  starts to be used) to the present time. Then, the guide output unit  2060  sets the direction in which the current inclination of the second camera  20  returns to the inclination of the second camera  20  when the field of view is correct as the direction in which the field of view of the second camera is to be oriented. The above-mentioned sensor is provided in the second camera  20 . 
     Alternatively, the information processing apparatus  2000  may analyze the image captured by the second camera  20  in time series to calculate the inclination direction of the camera. For example, the information processing apparatus  2000  calculates an optical flow between frames of the video generated by the second camera  20  and recognizes the movement direction of entire frames. Then, the information processing apparatus  2000  sets the direction in which the movement of all of the frames returns to the original position as the direction in which the field of view of the second camera  20  is to be oriented. 
     Example 2 of Guide 
     In  FIG. 13B , a guide  160 - 2  displayed on the display device  14  is the scenery (second captured image  50 ) that is currently included in the field of view of the second camera  20 . The user  30  can see the guide  160 - 2  and know what scenery is currently included in the field of view of the second camera  20 . 
     For example, as described above, it is assumed that the second camera  20  is used to capture an enlarged view of the head of a person. In contrast, in  FIG. 13A , the feet of the person are included in the guide  160 - 2  displayed on the display device  14 . Therefore, the field of view of the second camera  20  needs to be oriented upward. For this reason, the user  30  moves up the attachment position of the second camera  20  or adjusts the angle of view of the second camera  20  such that the second camera  20  is inclined upward until the head of the person is displayed in  160 - 2 . In this way, the user  30  can correct the field of view of the second camera  20  to a correct field of view. 
     Example 3 of Guide 
     A guide  160 - 3  illustrated in  FIG. 13C  is a frame indicating the current field of view of the second camera  20 . The user  30  that sees the guide  160 - 2  can recognize that the current field of view of the second camera  20  corresponds to a region surrounded by the guide  160 - 2  on the display device  14 . Then, the user  30  moves the attachment position of the second camera  20  or changes the angle of view of the second camera  20  until the guide  160 - 2  indicates the correct field of view of the second camera  20 . In this way, the user  30  can correct the field of view of the second camera  20  to a correct field of view. 
     Note that, the guide output from the guide output unit  2060  is not limited to the frame. For example, the guide output unit  2060  may color the region, instead of surrounding the region with the frame. In addition, for example, the guide output unit  2060  may not just display the guide, but may display the guide such that the guide blinks to call the user&#39;s attention. 
     The guide output unit  2060  compares the first captured image  40  with the second captured image  50  to detect which region of the first captured image  40  includes the scenery matched with the scenery in the second captured image  50 . Then, the guide output unit  2060  sets a region which corresponds to the detected region (hereinafter, referred to as a matched region) on the display device  14  as the region (to be represented by a guide  160 - 3 ) indicating the field of view of the second camera  20 . 
     Here, a specific method for displaying a region indicating the field of view of the second camera  20  on the display device  14  varies depending on whether the head-mounted display  10  is a transmissive head-mounted display or a non-transmissive head-mounted display. The transmissive head-mounted display is a head-mounted display in which a display device is transparent or translucent. The user of the transmissive head-mounted display can see, for example, the real scenery that is transmitted through the display device and is viewed and an AR image displayed on the display device at the same time to see a scene in which the AR image is superimposed on the real scenery. 
     In contrast, the non-transmissive head-mounted display is a head-mounted display in which a display device is not transparent. The non-transmissive head-mounted display  10  captures an image of surrounding scenery with the first camera  12 , generates the first captured image  40 , and displays the first captured image  40  on the display device  14 . The user  30  sees the first captured image  40  displayed on the display device  14  to see the surrounding scenery. The non-transmissive head-mounted display  10  displays, for example, an AR image on the display device  14  so as to be superimposed on the first captured image  40 . Therefore, the user can see a scene in which, for example, an AR image is superimposed on the real scenery. 
     It is assumed that the head-mounted display  10  is a transmissive head-mounted display. In this case, the guide output unit  2060  converts a matched region of the first captured image  40  into a region of the display device  14 , using the correspondence relationship between a position on the first captured image  40  and a position on the display device  14 . Then, the guide output unit  2060  displays information (for example, a frame) indicating the converted region of the display device  14  on the display device  14 . 
     Here, the correspondence relationship between a position on the first captured image  40  and a position on the display device  14  is predetermined on the basis of the relationship between the field of view of the first camera  12  and the display device  14 . Specifically, the correspondence relationship is predetermined using a parameter (a position with respect to the display device  14  or the angle of view) indicating the field of view of the first camera  12 . Information indicating the correspondence relationship may be set in the guide output unit  2060  in advance or may be stored in a storage region that can be accessed by the guide output unit  2060 . 
     In a case in which the head-mounted display  10  is a non-transmissive head-mounted display, the guide output unit  2060  superimposes, for example, an image of a frame indicating the matched region on the first captured image  40  displayed on the display device  14 . Then, a region corresponds to the field of view of the second camera  20  is displayed on the display device  14 . 
     Note that, the guide output unit  2060  may display the predetermined range  100  or the predetermined range  110  indicating the relationship information as a portion of the guide on the display device  14 .  FIGS. 14A and 14B  are diagrams illustrating a scene in which the predetermined range  100  or the predetermined range  110  is displayed as a portion of the guide on the display device  14 . In  FIG. 14A , the guide  160 - 3  and the predetermined range  100  are displayed as the guide on the display device  14 . The user can correct the field of view of the second camera  20  such that the predetermined range  100  is included in the guide  160 - 3 , thereby adjusting the field of view of the second camera  20  to be correct. 
     In contrast, in  FIG. 14B , the guide  160 - 3  and the predetermined range  110  are displayed as the guide on the display device  14 . The user can correct the field of view of the second camera  20  such that the predetermined range  110  is included in the guide  160 - 3  in the vertical direction, thereby adjusting the field of view of the second camera  20  to be correct. 
     Note that, in this example embodiment, the guide output from the guide output unit  2060  may also function as the notification information output from the notification unit  2040 . For example, the image of the arrow displayed on the display device  14  in  FIG. 13A  may function as a guide for correcting the field of view of the second camera  20  to a correct field of view and may also function as notification information for notifying the user  30  that the field of view of the second camera  20  is not correct. In this case, the information processing apparatus  2000  does not need to output the notification information separately from the guide. In this case, the information processing apparatus  2000  may not include the notification unit  2040 . 
     &lt;Example of Hardware Configuration&gt; 
     The information processing apparatus  2000  according to Example Embodiment 2 has, for example, the hardware configuration illustrated in  FIG. 3  which is the same as that of the information processing apparatus  2000  according to Example Embodiment 1. The storage  1080  according to Example Embodiment 2 stores a program for implementing each of the above-mentioned functions according to Example Embodiment 2. 
     Advantageous Effect 
     According to this example embodiment, information indicating that the field of view of the second camera  20  is not correct is notified and the guide for correcting the field of view of the second camera  20  is output. The use of the guide makes it possible for the user  30  to easily correct the field of view of the second camera  20 . 
     The example embodiments of the invention have been described above with reference to the drawings. However, the example embodiments are illustrative examples of the invention. The example embodiments may be combined with each other or various configurations other than the above may be used. 
     For example, the first camera  12  is not necessarily provided in the head-mounted display  10 .  FIG. 15  is a diagram illustrating a case in which the first camera  12  is provided in a place other than the head-mounted display  10 . In  FIG. 15 , the first camera  12  is fixed in the vicinity of the left ear of the user  30 . In addition, the first camera  12  may be fixed to, for example, a hat or general glasses worn by the user  30 . 
     Note that, it is preferable that the first camera  12  is fixed to the head (a part above the neck) of the user  30  such that the scenery in the first captured image  40  is close to the scenery in the field of view of the user  30 . However, the position where the first camera  12  is provided is not limited to the head of the user  30 . 
     In a case in which the first camera  12  is not provided in the head-mounted display  10 , the user  30  may not wear the head-mounted display  10 . In a case in which the user  30  does not wear the head-mounted display  10 , for example, the notification information generated by the notification unit  2040  or the guide generated by the guide output unit  2060  is output as a voice. For example, the notification information or the guide may be transmitted as text information or an image to a portable terminal of the user  30 . The user  30  can see the text information or the image displayed on a display device of the portable terminal to recognize that the field of view of the second camera  20  is not correct or to see the guide for correcting the field of view of the second camera  20 . 
     In addition, the user  30  may wear a contact lens including a display device, instead of the head-mounted display  10 . In this case, the information processing apparatus  2000  can treat the display device provided in the contact lens, similarly to the display device  14  of the head-mounted display  10 . In this case, the first camera  12  may be incorporated into the contact lens. 
     Next, an example of a reference example embodiment will be additionally described. 
     1. An information processing apparatus includes: a determination unit that determines whether a field of view of a second camera worn by a person is correct, on the basis of a first captured image which is generated by a first camera worn by the person, a second captured image generated by the second camera, and relationship information indicating a predetermined relationship to be satisfied between a field of view of the first camera and the field of view of the second camera; and a notification unit that, in a case in which the field of view of the second camera is determined to be incorrect, notifies that the field of view of the second camera is incorrect. The first camera is provided in a head-mounted display worn by the person and the second camera is provided in a part other than the head-mounted display. 
     2. In the information processing apparatus according to 1, the relationship information indicates a relationship in which a predetermined range of the field of view of the first camera is included in the field of view of the second camera. The determination unit determines whether the predetermined range of the field of view of the first camera is included in the field of view of the second camera, on the basis of the first captured image, the second captured image, and the relationship information. In a case in which the predetermined range of the field of view of the first camera is not included in the field of view of the second camera, the determination unit determines that the field of view of the second camera is incorrect. 
     3. In the information processing apparatus according to 2, the predetermined range of the field of view of the first camera indicates a range of the field of view of the first camera in a vertical direction or a horizontal direction. 
     4. In the information processing apparatus according to 1, in a case in which a person is included in the predetermined range of the field of view of the first camera, the relationship information indicates a relationship in which a predetermined part of the person is included in the field of view of the second camera. The determination unit determines whether the person is included in the predetermined range of the field of view of the first camera, on the basis of the first captured image and the relationship information. In a case in which the person is included in the predetermined range of the field of view of the first camera, the determination unit determines whether the predetermined part of the person is included in the field of view of the second camera, on the basis of the second captured image and the relationship information. In a case in which the predetermined part of the person is not included in the field of view of the second camera, the determination unit determines that the field of view of the second camera is incorrect. 
     5. The information processing apparatus according to any one of 1. to 4. further includes a guide output unit that outputs a guide for correcting the field of view of the second camera in a case in which the field of view of the second camera is determined to be incorrect. 
     6. In the information processing apparatus according to 5, the guide indicates a direction in which the field of view of the second camera is to be oriented. 
     7. In the information processing apparatus according to 5, the guide indicates the second captured image. 
     8. In the information processing apparatus according to 5, the guide is superimposed on the field of view of the first camera and indicates a current field of view of the second camera. 
     9. In the information processing apparatus according to 5. to 8, the guide output unit displays the guide on a display device provided in the head-mounted display. 
     10. A control method that is performed by a computer includes: a determination step of determining whether a field of view of a second camera worn by a person is correct, on the basis of a first captured image generated by a first camera worn by the person, a second captured image generated by the second camera, and relationship information indicating a predetermined relationship to be satisfied between a field of view of the first camera and the field of view of the second camera; and a notification step of, in a case in which the field of view of the second camera is determined to be incorrect, notifying that the field of view of the second camera is incorrect. The first camera is provided in a head-mounted display worn by the person and the second camera is provided in a part other than the head-mounted display. 
     11. In the control method according to 10, the relationship information indicates a relationship in which a predetermined range of the field of view of the first camera is included in the field of view of the second camera. In the determination step, it is determined whether the predetermined range of the field of view of the first camera is included in the field of view of the second camera, on the basis of the first captured image, the second captured image, and the relationship information. In a case in which the predetermined range of the field of view of the first camera is not included in the field of view of the second camera, it is determined that the field of view of the second camera is incorrect. 
     12. In the control method according to 11, the predetermined range of the field of view of the first camera indicates a range of the field of view of the first camera in a vertical direction or a horizontal direction. 
     13. In the control method according to 10, in a case in which a person is included in the predetermined range of the field of view of the first camera, the relationship information indicates a relationship in which a predetermined part of the person is included in the field of view of the second camera. In the determination step, it is determined whether the person is included in the predetermined range of the field of view of the first camera, on the basis of the first captured image and the relationship information. In a case in which the person is included in the predetermined range of the field of view of the first camera, it is determined whether the predetermined part of the person is included in the field of view of the second camera, on the basis of the second captured image and the relationship information. In a case in which the predetermined part of the person is not included in the field of view of the second camera, it is determined that the field of view of the second camera is incorrect. 
     14. The control method according to any one of 10. to 13. further includes a guide output step of outputting a guide for correcting the field of view of the second camera in a case in which the field of view of the second camera is determined to be incorrect. 
     15. In the control method according to 14, the guide indicates a direction in which the field of view of the second camera is to be oriented. 
     16. In the control method according to 14, the guide indicates the second captured image. 
     17. In the control method according to 14, the guide is superimposed on the field of view of the first camera and indicates a current field of view of the second camera. 
     18. In the control method according to any one of 14. to 17, in the guide output step, the guide is displayed on a display device provided in the head-mounted display. 
     19. A program causes a computer to perform each step of the control method according to any one of 10. to 18. 
     20. A head-mounted display includes: a first camera that performs imaging to generate a first captured image; a determination unit that determines whether a field of view of a second camera worn by a person that wears the head-mounted display is correct, on the basis of the first captured image, a second captured image generated by the second camera, and relationship information indicating a predetermined relationship to be satisfied between a field of view of the first camera and the field of view of the second camera; and a notification unit that, in a case in which the field of view of the second camera is determined to be incorrect, notifies that the field of view of the second camera is incorrect. The second camera is provided in a part other than the head-mounted display. 
     21. A body-worn camera that is worn by a person includes: a determination unit that determines whether a field of view of the body-worn camera is correct, on the basis of a first captured image which is generated by a camera provided in a head-mounted display worn by the person, a second captured image generated by the body-worn camera, and relationship information indicating a predetermined relationship to be satisfied between a field of view of the camera provided in the head-mounted display and the field of view of the body-worn camera; and a notification unit that, in a case in which the field of view of the body-worn camera is determined to be incorrect, notifies that the field of view of the body-worn camera is incorrect. The body-worn camera is provided in a part other than the head-mounted display.