Patent Publication Number: US-2023142255-A1

Title: Authentication device, authentication system, authentication method, andauthentication program

Description:
TECHNICAL FIELD 
     The present invention relates to an authentication device, an authentication system, an authentication method, and an authentication program that authenticates a target. 
     BACKGROUND ART 
     Various methods of authenticating a target are known. A physical key, such as classic waybill or a ticket, is one of the authentication methods. Patent literature 1 also describes key authentication, which authenticates an electronic key stored in a device such as an ID card. 
     However, key authentication is inconvenient because the target must carry a key in some way, and there is a high risk of unauthorized access due to theft or loss. In contrast, there is a method of authentication similar to the classic password, in which the target and the authenticator agree on keywords such as PIN, password, and responds to secret questions in advance, and the target is asked to enter the keywords from a keyboard or touch panel. This type of authentication method is hereinafter referred to as keyword authentication. 
     The keyword authentication is becoming popular because the authentication key is stored in the target&#39;s memory, thus eliminating the need for personal belongings. However, when keywords are input from a keyboard or touch panel, it is difficult for the target to input the keywords when the target is carrying luggage in both hands. The keyword authentication is also problematic because there is a high risk that a third party will intercept input from a keyboard or touch panel, leak keywords, and gain unauthorized access. 
     One possible solution to this problem is to have the target orally utter the keywords and obtain the input of the keywords via voice authentication. However, this method increases the risk of unauthorized access because keywords can be easily heard by a third party in the vicinity. 
     Also known is a method that uses eye movements as an alternative technique to keyword input from a keyboard or touch panel in situations where both hands are not available. Patent literature 2 describes a method of eye input communication using eye movements. Specifically, Patent literature 2 describes an authentication method that uses a camera to observe eye opening and closing, and authenticates the order of opening and closing of one eye, for example, “right, left, left, right,” as a substitute for a PIN, and a method that substitutes input from a keyboard or touch panel by using eye direction and blinking. 
     In addition, Patent literature 3 describes a method of performing user authentication processing using gaze input. In the case of gaze input, the gaze itself may be inferred by surrounding third parties from eye movements, but the exact direction of gaze cannot be determined without looking at the eyeballs from an angle close to the front of the face. 
     Therefore, since it is difficult to simultaneously steal both the movement of the eyeballs and the image to which the gaze is directed, this method is an effective method to solve the issue of the risk of unauthorized access. 
     In addition, various other biometric authentication methods are also known, in which biometric information such as fingerprints, face, and iris of the target is recorded in advance and used as a key for authentication (see, for example, Patent literatures 4 to 6). 
     Furthermore, in order to improve the security strength of authentication, a method of authentication using multiple factors has also been proposed. Patent literature 7 describes a multi-factor authentication method that uses multiple factors for authentication. In addition, Patent literature 8 describes a method that combines password authentication using eye gaze input and biometric authentication. 
     Even in face authentication, where it is difficult for a third party to spoof a person, there is a risk of spoofing using a photograph of the person&#39;s face or a three-dimensional doll that replicates the person&#39;s face to obtain authentication. A method for preventing such spoofing is described in Patent literature 9. In the method described in Patent literature 9, the target&#39;s face image is acquired multiple times to check for facial changes, and in the process, movements such as blinking or opening the mouth are required to confirm that the person is not a doll. 
     CITATION LIST 
     Patent Literature 
     PTL 1: Japanese Patent Laid-Open No. Sho 63-313288 
     PTL 2: Japanese Patent Laid-Open No. 2005-100366 
     PTL 3: Japanese Patent Laid-Open No. 2014-92941 
     PTL 4: Japanese Patent Laid-Open No. Sho 58-176781
 
PTL 5: Japanese Patent Laid-Open No. Sho 59-194274
 
     PTL 6: Japanese Patent Laid-Open No. 2001-34754 
     PTL 7: Japanese Patent Laid-Open No. 2009-71430 
     PTL 8: Japanese Patent Laid-Open No. 2006-277396 
     PTL 9: Japanese Patent Laid-Open No. Hei 11-339048 
     SUMMARY OF INVENTION 
     Technical Problem 
     On the other hand, when the order in which eyes are opened and closed is used as a substitute for the PIN as described in Patent literature 2, there is a high risk of unauthorized access because, as with voice, it is easy for a surrounding third party to steal the PIN. 
     In response to this problem, the method described in Patent literature 3 reduces the risk of unauthorized access because the user authentication process is performed using eye gaze input. However, with the method described in Patent literature 3, there is still a possibility of unauthorized access if the user authentication image is known to others. 
     On the one hand, the biometric authentication methods described above all have the advantage that they do not require ID cards or other personal belongings to be carried, and it is extremely difficult for a third party to steal the key and spoof the user. On the other hand, some biometric authentication methods require special input devices. For example, in the case of fingerprint or iris authentication, a special input device is required, and the target is required to place target&#39;s finger or eye on a certain position. Therefore, there is a problem of convenience during authentication for both the authenticator and the target. 
     On the other hand, among biometric authentication, face authentication does not require a special input device, and can authenticate images taken from a slightly distant position with a normal camera. It can be said that this is an extremely convenient authentication method that has the advantages of biometric authentication and does not pose the same problems as fingerprint or iris authentication. However, even this type of face authentication may reach its accuracy limit when the number of targets to be matched increases, and the problem of spoofing remains. 
     In the method described in Patent literature 8, authentication is performed using voiceprint information, face images, and palm prints, as well as password authentication using gaze input. However, the authentication method using voiceprint information and palm prints compromises convenience, and the problem of spoofing, as described above, still remains with authentication using face images. 
     In addition, Patent literature 9 also describes that the target is required to wait in front of the authentication device until the authentication device obtains a facial image multiple times to confirm that it is not a spoofing, or the target is required to blink or open his/her mouth as instructed. However, such responses are inconvenient for the target and impair comfort, resulting in reduced convenience. 
     Therefore, it is an exemplary object of the present invention is to provide an authentication device, an authentication system, an authentication method, and an authentication program that can detect spoofing of the target and authenticate the target with high accuracy, while improving the convenience of the authenticator and the target during authentication. 
     Solution to Problem 
     The authentication device according to the present invention is an authentication device that includes an output means which outputs a plurality of candidate responses to questions to the target on a display device, a response specification means which specifies a response to the question from among the candidate responses based on a target&#39;s gaze in a face image captured by an imaging device that captures a face image of the target, a response judgment means which makes a correctness or incorrectness judgment of the specified response, a face authentication means which performs target&#39;s face authentication from the face image captured by the imaging device, a biometric determination means which performs target&#39;s biometrics determination based on changes in the target&#39;s gaze detected from a plurality of the face image, and a target authentication means which authenticates the target based on results of the correctness or incorrectness judgment, the biometrics determination, and the face authentication. 
     The authentication system according to the present invention is an authentication system that includes an imaging device which captures a face image of the target, an output means which outputs a plurality of candidate responses to questions to the target on a display device, a response specification means which specifies a response to the question from among the candidate responses based on a target&#39;s gaze in the captured face image, a response judgment means which makes a correctness or incorrectness judgment of the specified response, a face authentication means which performs target&#39;s face authentication from the captured face image, a biometric determination means which performs target&#39;s biometrics determination based on changes in the target&#39;s gaze detected from a plurality of the face image, and a target authentication means which authenticates the target based on results of the correctness or incorrectness judgment, the biometrics determination, and the face authentication. 
     The authentication method according to the present invention is an authentication method that includes outputting a plurality of candidate responses to questions to the target on a display device, specifying a response to the question from among the candidate responses based on a target&#39;s gaze in a face image captured by an imaging device that captures a face image of the target, making a correctness or incorrectness judgment of the specified response, performing target&#39;s face authentication from the face image captured by the imaging device, performing target&#39;s biometrics determination based on changes in the target&#39;s gaze detected from a plurality of the face image, and authenticating the target based on results of the correctness or incorrectness judgment, the biometrics determination, and the face authentication. 
     The authentication program according to the present invention is a program that is applied to a computer that authenticates a target, and causes a computer to execute an output process of outputting a plurality of candidate responses to questions to the target on a display device, a response specification process of specifying a response to the question from among the candidate responses based on a target&#39;s gaze in a face image captured by an imaging device that captures a face image of the target, a response judgment process of making a correctness or incorrectness judgment of the specified response, a face authentication process of performing target&#39;s face authentication from the face image captured by the imaging device, a biometric determination process of performing target&#39;s biometrics determination based on changes in the target&#39;s gaze detected from a plurality of the face image, and a target authentication process of authenticating the target based on results of the correctness or incorrectness judgment, the biometrics determination, and the face authentication. 
     Advantageous Effects of Invention 
     According to the exemplary aspect of the present invention, it is possible to detect spoofing of the target and authenticate the target with high accuracy, while improving the convenience of the authenticator and the target during authentication. 
    
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         FIG.  1    It depicts a block diagram showing a configuration example of a first exemplary embodiment of an authentication system according to the present invention. 
         FIG.  2    It depicts a flowchart showing an operation example of an authentication system in the first exemplary embodiment. 
         FIG.  3    It depicts a block diagram showing a configuration example of a second exemplary embodiment of an authentication system according to the present invention. 
         FIG.  4    It depicts a flowchart showing an operation example of an authentication system in the second exemplary embodiment. 
         FIG.  5    It depicts a block diagram showing a configuration example of a third exemplary embodiment of an authentication system according to the present invention. 
         FIG.  6    It depicts a flowchart showing an operation example of an authentication system in the third exemplary embodiment. 
         FIG.  7    It depicts an explanatory diagram showing an example of operation when performing gaze input keyword authentication. 
         FIG.  8    It depicts an explanatory sequence diagram showing an example of operation using the authentication system. 
         FIG.  9    It depicts a block diagram showing an overview of an authentication device according to the present invention. 
         FIG.  10    It depicts a block diagram showing an overview of an authentication system according to the present invention. 
     
    
    
     DESCRIPTION OF EMBODIMENTS 
     In this exemplary embodiment, multiple authentication methods are used together to authenticate the target with high accuracy and to reduce the risk of spoofing. The combined use of authentication methods not only increases the accuracy of authentication, but also reduces the risk of spoofing. For example, it is assumed a method in which a PIN is used in addition to face authentication. In this case of this method, although it is possible to obtain the target&#39;s face photo and spoof the target against facial authentication, the PIN must also be obtained to be authenticated, which has the effect of greatly reducing the risk of spoofing. 
     However, simply using a combination of authentication methods may compromise advantages and convenience. For example, if face authentication is determined to be insufficiently accurate, key authentication, as described above, could be used as a second authentication factor. However, the addition of key authentication would compromise the major advantage of face authentication, which is the elimination of the need for personal belongings to be carried. 
     Another possible method is to use keyword authentication as a second authentication factor, as described above. However, since keyword authentication requires manual input, the advantage of face authentication, for example, that authentication can be performed even when the user is holding luggage in both hands, is lost. 
     Furthermore, fingerprint and iris authentication could be used as a second authentication factor. However, as mentioned above, fingerprint and iris authentication require a special input device, and thus, convenience for the authenticator is compromised. 
     Therefore, in this exemplary embodiment, the target of the user to be authenticated (hereinafter referred to as the “target”) is authenticated based on the results of the correctness or incorrectness judgment of the responses given by the target and the target&#39;s biometrics determination. The authentication in this exemplary embodiment includes the broad concept of authenticating the suitability of an individual, such as identifying the target and determining whether or not the target has authority. 
     First, a brief description of the features of this invention will be given. The first feature of this invention is that some question is asked to the target and multiple candidate responses to the question are presented at random locations on the display device. The target is then asked to gaze at the responses, and by authenticating the selected response from the direction of the target&#39;s gaze, the system authenticates whether the selected response is the correct response. In the following description, this method is referred to as gaze input keyword authentication. 
     The gaze input keyword authentication can be said to replace the manual input using a keyboard or touch panel with the gaze input with respect to the input of a keyword in the keyword authentication. This allows for highly accurate authentication of individuals and has the effect of allowing information to be input even when the target&#39;s hands are occupied, while maintaining the characteristics of keyword authentication, which is that the target does not need to carry an ID card or other personal belongings as is the case with key authentication. 
     Furthermore, it is compared the method in which keyword input in keyword authentication is performed by voice authentication with the method in which the gaze input keyword authentication is performed. In the gaze input keyword authentication, a third party in front of the target can identify the direction of the target&#39;s gaze, but cannot see the candidate responses on the display device. A third party behind the target can see the candidate responses on the display device, but not the direction of the target&#39;s gaze. Thus, the gaze input keyword authentication has the effect that there is very little risk of a third party in the vicinity being able to spy on the responses selected by the gaze. 
     This feature not only provides high security to the target of personal authentication. Specifically, the authenticator that performs personal authentication does not need to install walls or shields to block a furtive glance or eavesdropping by third parties, and can be used in open spaces with many third parties around, a convenience that is not available with general keyword authentication or keyword authentication using voice authentication. 
     Furthermore, the components necessary to implement this authentication method may include a display device that mainly presents candidate responses, a camera that takes pictures of the target, and a CPU (Central Processing Unit) that analyzes the direction of gaze. Therefore, the system can be implemented simply by installing an authentication program on a commercially available tablet or laptop PC. In this respect, the system provides a high level of convenience to the authenticator. 
     Furthermore, a second feature of the invention is the combination of the gaze input keyword authentication described above and face authentication of the target. The gaze input keyword authentication also does not require any personal belongings to be carried, is hands-free, and does not present the same convenience issues as fingerprint or iris authentication. Therefore, when the gaze input keyword authentication is used in combination with face authentication, it can be said that the advantages of face authentication are rarely compromised. Therefore, the gaze input keyword authentication has an effect that cannot be obtained by combining it with other authentication methods as a multi-factor authentication that augments face authentication. 
     In addition, both the gaze input keyword authentication and face authentication can share a single camera that captures images of the face. Therefore, the cost and construction for augmenting face authentication with multi-factor authentication are low, and face authentication and eye direction measurement can be performed at the same time. Thus, the burden on both the target and the authenticator can be reduced, a practical effect that is not a mere combination. 
     Furthermore, a third feature of the invention, in addition to the features described above, is to verify that the gaze of the person whose face is authenticated is moving by performing face authentication and measurement of the gaze of the target selecting a response multiple times in parallel. This allows verification that the target is a living body of a person. 
     Both face authentication and the gaze key word authentication are authentication methods that make it difficult for a third party to spoof the user. However, there is still a risk that a third party could spoof a person with a time lag, for example, by performing face recognition using a photograph of the person&#39;s face or a three-dimensional doll that replicates the face, and then a third party taking over and performing the gaze input keyword recognition. 
     In contrast, in this exemplary embodiment, the face authentication and the measurement of the target&#39;s gaze to select a response are performed multiple times in parallel to verify that the gaze of the person whose face is authenticated is moving. This has the effect of eliminating spoofing by a mug shot of the person&#39;s face or a three-dimensional doll with a duplicated face. 
     To add, it is not possible to verify that the person whose face is authenticated is a living body simply by performing multiple authentications in face authentication as mentioned in the first feature. In addition, if the second feature, the gaze input keyword authentication, only verifies that the person is a living body based on gaze movement, there is still a risk of unauthorized access due to leakage of keywords. On the other hand, the combination of the three features described above can cover all of these issues, and thus has a special effect that cannot be obtained by simply combining them. 
     Other features of the invention include: presenting candidate responses on the display device, obtaining the time when the target selects the response by moving target&#39;s gaze and the result of face authentication using a face image obtained at the same time, and thereby verifying that the person is the living body matched by face authentication. 
     By obtaining the results of face authentication at the same time as the time when the target selects a response by moving the target&#39;s gaze and verifying that the target is the living body matched by face authentication, this has the effect of preventing spoofing due to the time difference as described above. 
     A further feature of the invention is to check a relative angle change of the gaze with respect to the direction of a face while the target moves the gaze and selects a response. This makes it possible to verify that the target is the living body matched by face authentication. 
     For example, a third party may control the direction of the 3D doll&#39;s gaze by changing the angle of the doll&#39;s entire face and spoof the gaze input keyword authentication while using a 3D doll that replicates the person&#39;s face to spoof face authentication. 
     However, in this exemplary embodiment, even for such a high degree of spoofing, the relative angle change of the gaze with respect to the direction of the face is confirmed while the target moves the gaze to select a response. Such a configuration enables verification that the living body is moving his/her gaze, rather than the entire face of the photograph or three-dimensional doll, and thus has the effect of suppressing such a high degree of spoofing as described above. 
     Furthermore, even when the additional features described above are realized, the required components remain the same. In other words, it is possible to realize the features described above simply by installing an authentication program on a commercially available tablet or laptop PC. These features may be realized using multiple devices, circuits, and programs. If the service as a whole satisfies the components to realize the features described above, it can provide high reliability and convenience to the authenticator and the target while maintaining the same effects as described above. 
     The following is a description of the exemplary embodiment of the invention with reference to the drawings. 
     Exemplary Embodiment 1 
       FIG.  1    is a block diagram showing a configuration example of a first exemplary embodiment of an authentication system according to the present invention. The authentication system  100  in this exemplary embodiment includes an authentication device  10 , an imaging device  20 , and a display device  30 . The imaging device  20  is installed in the vicinity of the display device  30  and at a position that enables imaging of the target&#39;s viewing movement toward the display device  30 . 
     The imaging device  20  is a device that captures a target&#39;s face image. The imaging device  20  may, for example, obtain an image of each frame captured in chronological order as a video image as the target&#39;s face image. The imaging device  20  may capture the target&#39;s face image at the timing when it detects a person within the imaging range, or may capture the target&#39;s face image at the timing when the target performs some action to the authentication device  10 . In the example shown in  FIG.  1   , the authentication system  100  is shown with two imaging devices  20 . However, the system may include only one imaging device  20 . 
     The display device  30  outputs various information according to the instructions of the output unit  13  described below. The display device  30  is realized, for example, by a display device or a tablet. 
     The authentication device  10  includes a storage unit  11 , an input unit  12 , an output unit  13 , a response specification unit  14 , a response judgment unit  15 , a face authentication unit  16 , a biometric determination unit  17 , and a target authentication unit  18 . 
     The storage unit  11  stores various information used by the authentication device  10  for processing. For example, the storage unit  11  may store face images and features used for authentication by the face authentication unit  16  described below. The storage unit  11  may also store questions to be asked to the target and candidate responses to those questions. Here, the candidate response is information that includes a correct response to the question and an incorrect response to the question. The questions may be prepared for each identified target. The storage unit  11  is realized by, for example, a magnetic disk. 
     The input unit  12  accepts input of a face image of a target captured by the imaging device  20 . For example, if there are multiple imaging devices  20 , the input unit  12  may accept input of the face image along with information identifying the imaging device  20  that captured the face image. 
     The output unit  13  outputs multiple candidate responses to questions to be asked to the target on the display device  30 . Specifically, when the target appears, the output unit  13  outputs a question to the target and multiple candidate responses to the question at a random position on the display device  30 , and requests the target to view the responses. By outputting multiple candidate responses at random locations, it is possible to move the gaze of the target checking the response in various directions, making it easier for the biometric determination unit  17 , described below, to make a judgment. 
     The content of the questions and candidate responses are arbitrary and may be predetermined. The output unit  13  may, for example, ask questions such as “What is your ID number?” and “What is your PIN?” etc. on the screen, and an icon with numbers from  0  to  9  may be output at a random position on the display device as multiple candidate responses to the question. However, the questions and the candidate responses are not limited to this example. 
     The questions do not have to be output to the display device  30 , but may be output from a speaker (not shown), for example, by voice. 
     If the target is authenticated by the face authentication unit  16  (described below), the output unit  13  may output a target-specific question and a plurality of candidate responses corresponding to the question on the display device  30 . Specifically, the output unit  13  may output a secret question created by the target and candidate responses to that question. For example, the output unit  13  may output a secret question, such as “What is the name of the elementary school you graduated from?” or “What is your mother&#39;s maiden name?”, prepared in advance by the person whose features match the face image, and the candidate response that is a response (and an incorrect response) to the question. By using such questions and candidate responses, it is possible to increase the security of authentication. 
     The response specification unit  14  specifies the response to the question from among multiple candidate responses based on the target&#39;s gaze in the captured face image. In other words, the response specification unit  14  measures the direction of gaze from the face image and specifies the selected response based on the direction of the target&#39;s gaze. 
     The method of specifying the position to which the target gazes based on the target&#39;s gaze is arbitrary. For example, the response specification unit  14  may specify the position at which the target gazes at the display device  30  using the method described in Patent literature 2. Specifically, the response specification unit  14  may measure the direction of the target&#39;s gaze from the position of the target&#39;s eyes, and may specify the candidate response output at the position where a direction vector of the gaze starting from the target&#39;s eye position intersects with the display unit  30  as the response selected by the target. 
     Since a person&#39;s gaze actually fluctuates, the response specification unit  14  may consider the candidate response at the position where the target&#39;s gaze remains for a certain time as the response selected by the target. The response specification unit  14  may also consider the candidate response at the position indicated by the target&#39;s gaze just before the target blinked as the response selected by the target. By allowing such fluctuation, the accuracy of specifying the response selected by the target can be improved. 
     The response judgment unit  15  makes a correctness or incorrectness judgment of the specified response. Specifically, the response judgment unit  15  compares the response selected by the target with the correct response registered in advance, and judges whether the response is correct or incorrect. Based on the judgment result, the response judgment unit  15  judges that the response is authenticated if it is correct, and judges that the response is not authenticated if it is incorrect. 
     The face authentication unit  16  performs target&#39;s face authentication from the captured face image. The method by which the face authentication unit  16  authenticates the target&#39;s face is arbitrary. For example, the face authentication unit  16  may perform face authentication by extracting facial features from the face image and determining whether or not the features match the facial features of a person stored in the storage unit  11  in advance. 
     The biometric determination unit  17  performs target&#39;s biometrics determination based on changes in the target&#39;s gaze detected from a plurality of face images captured. More precisely, the biometric determination unit  17  determines the target&#39;s biometrics based on changes in the direction of the target&#39;s gaze detected in the plurality of face images captured in chronological order. 
     Specifically, the biometric determination unit  17 , for example, receives the face images captured by the imaging device  20  in chronological order, and when the direction of the target&#39;s gaze in the received face images is changing, the biometric determination unit  17  may determine that the target is a living body. The biometric determination unit  17  may, for example, continue the authentication process by the face authentication unit  16  during the gaze input keyword authentication (i.e., during the processing of the response specification unit  14  and response judgment unit  15 ) and accept the results of that process to perform biometric determination. In other words, by repeating face recognition while the target is moving his/her gaze to the output candidate responses in the gaze input keyword authentication, the biometric determination unit  17 , as a result, can automatically verify that the face image authenticated by the facial recognition is the living body whose gaze is moved. 
     In other words, by performing the gaze input keyword authentication and face authentication in parallel, the target&#39;s gaze inevitably moves, then the biometric determination unit  17  can use this movement in gaze as a factor in biometric determination. 
     The target authentication unit  18  authenticates the target based on the results of the correctness or incorrectness judgment by the response judgment unit  15 , the biometric determination by the biometric determination unit  17 , and the face authentication by the face authentication unit  16 . Specifically, when the response is determined to be correct by the response judgment unit  15 , the target is determined to be a living body by the biometric determination unit  17 , and the target is authenticated by the face authentication unit  16 , then the target authentication unit  18  authenticates the target authenticated by the face authentication unit  16  as the appropriate target, and denies the target when even one of the above judgments or authentications has not been made. 
     In this exemplary embodiment, the case in which the authentication system  100  includes two imaging devices  20  is shown. Therefore, the response specification unit  14  specifies the response using the image (first face image) captured by a first imaging device, and the face authentication unit  16  may perform target&#39;s face authentication using the image (second face image) captured by a second imaging device. In this way, by providing imaging devices  20  that capture a face image for each process, it is possible to use the appropriate image for each process. 
     The input unit  12 , the output unit  13 , the response specification unit  14 , the response judgment unit  15 , the face authentication unit  16 , the biometric determination unit  17 , and the target authentication unit  18  are provided by a computer processor (for example, CPU (Central Processing Unit), GPU (Graphics Processing Unit) operating according to the program (authentication program). 
     For example, a program may be stored in the storage unit  11 , and the processor may read the program and, according to the program, the input unit  12 , the output unit  13 , the response specification unit  14 , the response judgment unit  15 , the face authentication unit  16 , the biometric determination unit  17 , and the target authentication unit  18 . In addition, the functions of the input unit  12 , the output unit  13 , the response specification unit  14 , the response judgment unit  15 , the face authentication unit  16 , the biometric determination unit  17 , and the target authentication unit  18  may be provided in SaaS (Software as a Service) format. 
     The input unit  12 , the output unit  13 , the response specification unit  14 , the response judgment unit  15 , the face authentication unit  16 , the biometric determination unit  17 , and the target authentication unit  18  may each be realized by dedicated hardware. In addition, some or all of the components of each device may be realized by a general-purpose circuit (circuitry) or a dedicated circuit, a processor, etc., or a combination of these. They may be configured by a single chip or by multiple chips connected via a bus. Some or all of the components of each device may be realized by a combination of the above-mentioned circuits, etc. and programs. 
     In the case where some or all of the components of the input unit  12 , the output unit  13 , the response specification unit  14 , the response judgment unit  15 , the face authentication unit  16 , the biometric determination unit  17 , and the target authentication unit  18  are realized by a plurality of information processing devices, circuits, or the like, the plurality of information processing devices, circuits, or the like may be centrally located or distributed. For example, the information processing devices, circuits, etc. may be realized as an embodiment where each of which is connected via a communication network, such as a client-server system, a cloud computing system, etc. 
     Next, an operation of the authentication system  100  in this exemplary embodiment will be described.  FIG.  2    is a flowchart showing an operation example of an authentication system  100  in this exemplary embodiment. 
     The output unit  13  outputs a plurality of candidate responses to the questions to be asked to the target on the display device (step S 1 ). Then, when the imaging device  20  captures the target&#39;s face image, the input unit  12  obtains the captured face image for the purpose of performing the gaze input keyword authentication (step S 2 ). The response specification unit  14  specifies a response to the question from among the candidate responses based on the target&#39;s gaze in the captured face image. That is, the response specification unit  14  measures the direction of the gaze (step S 3 ) and recognizes the selected response based on the direction of the gaze (step S 4 ). Steps S 2  and S 3  are repeated until a response is authenticated. 
     The response judgment unit  15  makes a correctness or incorrectness judgment of the specified response. That is, the response judgment unit  15  judges the correctness of the response (step S 5 ). If the response is not correct (No in step S 5 ), the authentication device  10  denies authentication. 
     Meanwhile, in parallel with the process from step S 1  to step S 5 , when the imaging device  20  captures a face image of the target, the input unit  12  obtains the captured face image for face authentication (step S 6 ). The imaging device  20  may be different for the gaze input keyword authentication and face authentication. The face authentication unit  16  performs target&#39;s face authentication from the captured face image. Specifically, the face authentication unit  16  extracts features from the face image (step S 7 ). Then, face authentication unit  16  determines whether the extracted features match the registered features (step S 8 ). If the extracted features do not match the registered features (No in step S 8 ), the authentication device  10  denies authentication. The process from step S 6  to step S 8  is repeated while the features are judged to match. 
     When all processing has been performed correctly (Yes in step S 9 ), the target authentication unit  18  determines that the target has been authenticated. That is, the target authentication unit  18  determines that the target has been authenticated when the responses are correct (Yes in step S 5 ) and the extracted features match the registered features (Yes in step S 8 ). On the other hand, if any part of the process was not performed correctly (No in step S 9 ), the target authentication unit  18  denies the authentication. 
     As described above, in this exemplary embodiment, the output unit  13  outputs a plurality of candidate responses to questions to the target on the display device, and when the response specification unit  14  specifies a response to the question from among the candidate responses based on the target&#39;s gaze in the face image captured by the imaging device  2 , the response judgment unit  15  makes a correctness or incorrectness judgment of the specified response. On the other hand, the face authentication unit  16  performs target&#39;s face authentication from the face image captured by the imaging device  20 , and the biometric determination unit  17  performs target&#39;s biometrics determination based on changes in the target&#39;s gaze detected from a plurality of the face image. The target authentication unit  18  authenticates the target based on the results of the correctness or incorrectness judgment, the biometric determination, and the face authentication. Thus, the target can be authenticated with high accuracy by detecting spoofing of the target while improving the convenience of the authenticator and the target&#39;s authentication. 
     Specifically, the authentication device  10  in this exemplary embodiment can provide authentication and anti-spoofing technology that authenticates individuals with high accuracy, while at the same time providing a low risk of unauthorized access or spoofing and high convenience for both the target and the authenticator. The first reason for this is that the combination of face authentication and the gaze input keyword authentication can authenticate individuals with high accuracy. 
     The second reason is that the risk of unauthorized access is minimized by using the target&#39;s biometric information in the form of a face image and the information in the target&#39;s memory in the form of keywords as the keys to authentication. Furthermore, the gaze that can be specified from a part of the face image can be used as a movement to select a keyword in the memory, and based on this movement, it is verified that the person is a living body, making it extremely difficult to gain unauthorized access or spoofing. 
     The third reason is that the target only needs to gaze at the responses to the questions presented on the display device for a short period of time, a small burden, in order to perform the two authentications and spoofing prevention described above. In addition, the target does not need to carry personal belongings, is hands-free, and does not need to worry about a furtive glance or eavesdropping by surrounding third parties, making the system extremely convenient. 
     The fourth reason is that the authenticator only needs to install a display device and a camera to capture face images in order to perform the two authentications and spoofing prevention described above. This enables highly accurate multi-factor authentication and spoofing prevention in a short period of time and is extremely convenient because it does not require the installation of walls or shields to prevent a furtive glance or eavesdropping by surrounding third parties. For example, commercially available smartphones, tablets, and laptop 
     PCs are often equipped with a display device and a camera that captures facial images. Therefore, the authenticator can realize the authentication device  10  of this exemplary embodiment by installing the program in these devices. 
     Exemplary Embodiment 2 
     Next, a second exemplary embodiment of the authentication system according to the present invention will be described. This exemplary embodiment describes a method of preventing spoofing using time differences. First, an overview of this exemplary embodiment will be described. In this exemplary embodiment, a face image for the gaze input keyword authentication is obtained at the same time as the face image for face authentication is obtained. The spoofing using the time difference is prevented by performing face authentication using a face image at the same time as the time when the target moves his/her gaze and selects an answer. 
       FIG.  3    is a block diagram showing a configuration example of a second exemplary embodiment of an authentication system according to the present invention. The authentication system  200  of this exemplary embodiment includes an authentication device  110 , an imaging device  20 , and a display device  30 . The configuration of the imaging device  20  and the display device  30  is the same as in the first exemplary embodiment. 
     The authentication device  110  includes a storage unit  11 , an input unit  12 , an output unit  13 , a response specification unit  24 , a response judgment unit  15 , a face authentication unit  26 , a biometric determination unit  17 , and a target authentication unit  28 . In other words, in this exemplary embodiment of authentication device, the processing performed by the response specification unit  24 , the face authentication unit  26 , and the target authentication unit  28  differ in part from the response specification unit  14 , the face authentication unit  16 , and the target authentication unit  18  in the first exemplary embodiment, respectively. Otherwise, they are the same as in the first exemplary embodiment. 
     The response specification unit  24  obtains response time at which the target specified the response, in addition to the process performed by the response specification unit  14  of the first exemplary embodiment. The face authentication unit  26  obtains a result of the face authentication performed at the same time as the response time, in addition to the process performed by the face authentication unit  16  of the first exemplary embodiment. The target authentication unit  28  then authenticates that the target is a living body matched by the face authentication. 
     In the case of a single imaging device  20 , the same frame image should be used for both the face image for the gaze input keyword authentication and the face image for face authentication. 
     The input unit  12 , the output unit  13 , the response specification unit  24 , the response judgment unit  15 , the face authentication unit  26 , the biometric determination unit  17 , and the target authentication unit  28  are provided by a computer processor operating according to the program (authentication program). 
     Next, an operation of the authentication system  200  in this exemplary embodiment will be described.  FIG.  4    is a flowchart showing an operation example of an authentication system  100  in this exemplary embodiment. The flowchart shown in  FIG.  4    is different from the flowchart shown in  FIG.  2    in that the time to obtain the face image in step S 2  and step S 6  is the same. Otherwise, the flowchart is the same as the flowchart shown in  FIG.  2   . This does not preclude the flowchart shown in  FIG.  2    from having the same time for obtaining face images in steps S 2  and S 6 . 
     As described above, in addition to the configuration of the first exemplary embodiment, in this exemplary embodiment, the response specification unit  24  obtains the response time at which the target specified the response, the face authentication unit  26  obtains the result of the face authentication performed at the same time as the response time, and the target authentication unit  28  authenticates that the target is a living body matched by the face authentication. Thus, in addition to the effect of the first exemplary embodiment, the effect of suppressing spoofing can be enhanced. 
     Exemplary Embodiment 3 
     Next, a third exemplary embodiment of the authentication system according to the present invention will be described. This exemplary embodiment describes a more specific configuration that prevents spoofing. First, an overview of this exemplary embodiment will be described. In this exemplary embodiment, the process of obtaining a target&#39;s face image and measuring the direction of the target&#39;s gaze and the direction of the face from that image is repeated several times. For this result, a relative angle change between the direction of gaze and the direction of the face is checked and if the change is greater than a certain level, it is judged positive (i.e., not spoofing), and if the change is within the measurement error, it is judged negative (i.e., spoofing). 
     The reasons for this determination are as follows. In fact, when searching for the correct response among the candidate responses presented on the display device, it is common for humans to try to find the response quickly by moving their gaze widely while making small movements in the direction of the entire face. Therefore, by checking the change in the relative angle between the direction of the gaze and the direction of the face, it is possible to verify that the obtained face image is that of a living body with higher accuracy and ease. This feature indicates that highly accurate face authentication and highly accurate spoofing prevention can be performed simultaneously during one action of searching for a response by the target. In other words, this is a special effect, not a mere combination, for the convenience of the target and the accuracy requirements of the authenticator. 
       FIG.  5    is a block diagram showing a configuration example of a third exemplary embodiment of an authentication system according to the present invention. The authentication system  300  of this exemplary embodiment includes an authentication device  210 , an imaging device  20 , and a display device  30 . The configuration of the imaging device  20  and the display device  30  is the same as in the first and second exemplary embodiments. 
     The authentication device  210  includes a storage unit  11 , an input unit  12 , an output unit  13 , a response specification unit  14 , a response judgment unit  15 , a face authentication unit  16 , a biometric determination unit  37 , and a target authentication unit  18 . In other words, in this exemplary embodiment of authentication device, the processing performed by the biometric determination unit  37  differs in part from the biometric determination unit  17  in the first exemplary embodiment. Otherwise, they are the same as in the first exemplary embodiment. For each configuration of the second exemplary embodiment, the biometric determination unit  37  may be used instead of the biometric determination unit  17 . 
     The biometric determination unit  37  detects a relative angle change of the gaze with respect to the direction of a face while the target moves the gaze and selects a response, and performs the target&#39;s biometrics determination. The biometric determination unit  37  may determine that the target is a living body when detecting a change greater than a predetermined amount of change, as described above. 
     The input unit  12 , the output unit  13 , the response specification unit  14 , the response judgment unit  15 , the face authentication unit  16 , the biometric determination unit  37 , and the target authentication unit  18  are provided by a computer processor operating according to the program (authentication program). 
     Next, an operation of the authentication system  300  in this exemplary embodiment will be described.  FIG.  6    is a flowchart showing an operation example of an authentication system  300  in this exemplary embodiment. The processing from step S 1  to step S 8  is the same as in the first exemplary embodiment. As in the second exemplary embodiment, the time to obtain the face image in step S 2  and step S 6  may be the same. 
     In this exemplary embodiment, the processing from step S 10  to step S 12  is performed in parallel with processing from step S 1  to step S 5  and from step S 6  to step S 8 . Specifically, the biometric determination unit  37  obtains a face image (Step S 10 ) and measures the direction of gaze and the direction of face (Step S 11 ). Repeating the process from step S 10  to step S 11 , the biometric determination unit  37  check the relative angle change (step S 12 ). 
     If the relative angle change is not greater than a predetermined value (No in step S 12 ), the authentication device  210  denies the authentication. On the other hand, if the relative angle change is greater than the predetermined value (Yes in step S 12 ), the target authentication unit  18  authenticates the target based on the results of the correctness or incorrectness judgment, the biometric determination, and the face authentication (Step S 9 ). 
     As explained in the second exemplary embodiment, the same frame face image captured by the same imaging device  20  may be used for both face authentication and the gaze input keyword authentication. 
     As described above, in addition to the configuration of the first exemplary embodiment, in this exemplary embodiment, the biometric determination unit  37  detects a relative angle change of the gaze with respect to the direction of a face while the target moves the gaze and selects a response, and performs the target&#39;s biometrics determination. Therefore, in addition to the effect of the first exemplary embodiment, the effect of suppressing spoofing can be enhanced. 
     Next, it is explained a specific example using the authentication system  100  of the first exemplary embodiment.  FIG.  7    is an explanatory diagram showing an example of operation when performing gaze input keyword authentication. When the target  31  appears in front of the authentication device  10 , the output unit  13  outputs a plurality of question candidates, such as “What&#39;s your ID number?”, “What&#39;s your PIN number?”, at random positions on the screen of the display device  30 . Then, the imaging device  20  captures the face image of the target  31 , and the analysis unit  32  including the response specification unit  14  and the response judgment unit  15  specifies the response selected by the target  31  based on the direction of his/her gaze  33 . The analysis unit  32  then checks the specified response against the correct response registered in advance, and makes a correctness or incorrectness judgment. With this correctness or incorrectness judgment, the authentication device  10  authenticates if the response is correct, and denies if the response is incorrect. 
     The authentication system  200  of the second exemplary embodiment and the authentication system  300  of the third exemplary embodiment are processed in the same manner. By handling such systems as a single unit, the effect is that installation and maintenance are easier than with individual components. For example, the imaging device  20  and the analysis unit described above can be shared for each of the uses performed in each of the above exemplary embodiments. 
     Next, an example of operation of the authentication system when used for authentication services is described.  FIG.  8    is an explanatory sequence diagram showing an example of operation using the authentication system. The example shown in  FIG.  8    illustrates the operation when the authentication system of the present invention is used as an authentication service  418  when the target  417  uses the interlocking service  419 . In other words, as illustrated in  FIG.  8   , in this operation example, it is assumed that there are three objects: the target  417 , the authentication service  418 , and the interlocking service  419 , and by exchanging and executing messages between these three objects, the authentication service as a whole is provided. 
     The interlocking service  419  includes, for example, an ATM (automatic teller machine) service that allows deposits and withdrawals according to the results of authentication, and an admission control service that opens and closes doors and gates according to the results of authentication. 
     First, when the target  417  appears at the authentication system, the authentication service  418  detects this in some way and starts the authentication service. Specifically, for example, the authentication service  418  may recognize the start of the authentication service when the target  417  presses an authentication start button, or the authentication service  418  may detect a human face of a certain size or larger in the image of the camera (imaging device  20 ) and recognize the appearance of the target  417 . In the example shown in  FIG.  8   , this is generalized to notation as the found message  420  being sent to the authentication service  418  from an object not on the diagram. 
     When receiving the found message  420 , the authentication service  418  outputs a question and a candidate response as an operation  421 . Specifically, the authentication service  418  sets questions such as “What is your ID number?” and “What is your password?” and numbers from  0  to  9  as candidate responses, and outputs the candidate response at random locations on display device  30 . 
     Here, in operation  421 , the authentication service  418  may perform face authentication of the target, set a secret question pre-registered, such as “What is the name of the elementary school you graduated from?”, by the target estimated from the result, and set a pre-registered answer, etc. as a candidate answer and output them. 
     The authentication service  418  then sends the set questions as a message  422  to the target  417 . Specifically, the authentication service  418  may, for example, output the question audibly through a speaker device or display the question on the display device  30 . 
     The target  417  who received the question as a message  422  looks for a correct response among the candidate responses output at a random position on the display device  30  The target  417 , and performs operation  423  to gaze at the correct response. In this operation  423 , the target  417  repeatedly sends the message  424  to the authentication service  418  in the form of the direction of gaze. In parallel with operation  423 , the authentication service  418  repeatedly captures the face image of the target  417  with a camera (imaging device  20 ). In the example shown in  FIG.  8   , the face image to be obtained is denoted as a found message  425  sent from an object not on the diagram to the authentication service  418 . 
     When receiving the message  424  and the message  425 , the authentication service  418  performs, as operation  426 , the gaze input keyword authentication, which authenticates and matches responses based on the direction of gaze, the face authentication, which extracts and matches features from the face image, and checking to prevent spoofing based on changes in the relative angle of gaze and face direction that changes over time. The authentication service  418  then notifies the authentication result to the interlocking service  419  as a message  427 , and also replies to the target  417  as a message  428 . The authentication service  418  may communicate the authentication results to the target  417 , for example, by means of an announcement tone or alarm tone. 
     As illustrated in  FIG.  8   , the action required of the target  417  is to select the candidate responses shown in operation  423 . Thus, in the exemplary embodiment described above, multiple authentications can be performed simultaneously by having the target select a candidate response. It can also provide high reliability and convenience to both the target and the authenticator. The above-described exemplary embodiment may be realized in any device or equipment in which it is divided. 
     Next, an overview of the present invention will be described.  FIG.  9    is a block diagram showing an overview of an authentication device according to the present invention. The authentication device  80  according to the present invention is an authentication device (for example, the authentication device  10 ) which authenticates a target, comprises an output means  81  (e.g., output unit  13 ) which outputs a plurality of candidate responses to questions to the target on a display device (e.g., display device  30 ), a response specification means  82  (e.g., response specification unit  14 ) which specifies a response to the question from among the candidate responses based on a target&#39;s gaze in a face image captured by an imaging device (e.g., imaging device  20 ) that captures a face image of the target, a response judgment means  83  (e.g., response judgment unit  15 ) which makes a correctness or incorrectness judgment of the specified response, a face authentication means  84  (e.g., face authentication unit  16 ) which performs target&#39;s face authentication from the face image captured by the imaging device, a biometric determination means  85  (e.g., biometric determination unit  17 ) which performs target&#39;s biometrics determination based on changes in the target&#39;s gaze detected from a plurality of the face image, and a target authentication means  86  (e.g., target authentication unit  18 ) which authenticates the target based on results of the correctness or incorrectness judgment, the biometrics determination, and the face authentication. 
     Such a configuration can detect spoofing of the target and authenticate the target with high accuracy, while improving the convenience of the authenticator and the target during authentication. 
     The response specification means  82  may obtain response time at which the target specified the response, the face authentication means  84  may obtain a result of the face authentication performed at the same time as the response time, and the target authentication means  86  may authenticate that the target is a living body matched by the face authentication. 
     The biometric determination means  85  may detect a relative angle change of the gaze with respect to the direction of a face while the target moves the gaze and selects a response, and perform the target&#39;s biometrics determination. 
     The output means  81  may output a plurality of candidate responses corresponding to the target-specific questions authenticated by the face authentication on the display device. 
     The response specification means  82  may specify a response based on the target&#39;s gaze in a first face image captured by a first imaging device, and the face authentication means  84  may perform target&#39;s face authentication from a second face image captured by a second imaging device. 
       FIG.  10    is a block diagram showing an overview of an authentication system according to the present invention. The authentication system  90  according to the present invention is an authentication system (for example, the authentication system  100 ) which authenticates a target, comprises 
     Such a configuration can also detect spoofing of the target and authenticate the target with high accuracy, while improving the convenience of the authenticator and the target during authentication. 
     A part of or all of the above example embodiment may also be described as, but not limited to, the following supplementary notes. 
     (Supplementary note 1) An authentication device which authenticates a target comprising: an output means which outputs a plurality of candidate responses to questions to the target on a display device; a response specification means which specifies a response to the question from among the candidate responses based on a target&#39;s gaze in a face image captured by an imaging device that captures a face image of the target; a response judgment means which makes a correctness or incorrectness judgment of the specified response; a face authentication means which performs target&#39;s face authentication from the face image captured by the imaging device; a biometric determination means which performs target&#39;s biometrics determination based on changes in the target&#39;s gaze detected from a plurality of the face image; and a target authentication means which authenticates the target based on results of the correctness or incorrectness judgment, the biometrics determination, and the face authentication. 
     (Supplementary note 2) The authentication device according to Supplementary note 1, wherein the response specification means obtains response time at which the target specified the response, the face authentication means obtains a result of the face authentication performed at the same time as the response time, and the target authentication means authenticates that the target is a living body matched by the face authentication. 
     (Supplementary note 3) The authentication device according to Supplementary note 1 or 2, wherein the biometric determination means detects a relative angle change of the gaze with respect to the direction of a face while the target moves the gaze and selects a response, and performs the target&#39;s biometrics determination. 
     (Supplementary note 4) The authentication device according to any one of Supplementary notes 1 to 3, wherein the output means outputs a plurality of candidate responses corresponding to the target-specific questions authenticated by the face authentication on the display device. 
     (Supplementary note 5) The authentication device according to any one of Supplementary notes 1 to 4, wherein the response specification means specifies a response based on the target&#39;s gaze in a first face image captured by a first imaging device, and the face authentication means performs target&#39;s face authentication from a second face image captured by a second imaging device. 
     (Supplementary note 6) An authentication system which authenticates a target comprising: an imaging device which captures a face image of the target; an output means which outputs a plurality of candidate responses to questions to the target on a display device; a response specification means which specifies a response to the question from among the candidate responses based on a target&#39;s gaze in the captured face image; a response judgment means which makes a correctness or incorrectness judgment of the specified response; a face authentication means which performs target&#39;s face authentication from the captured face image; a biometric determination means which performs target&#39;s biometrics determination based on changes in the target&#39;s gaze detected from a plurality of the face image; and a target authentication means which authenticates the target based on results of the correctness or incorrectness judgment, the biometrics determination, and the face authentication. 
     (Supplementary note 7) The authentication system according to Supplementary note 6, further comprising a plurality of imaging devices which capture the face image of the target, wherein the response specification means specifies a response based on the target&#39;s gaze in a first face image captured by a first imaging device, and the face authentication means performs target&#39;s face authentication from a second face image captured by a second imaging device. 
     (Supplementary note 8) An authentication method which authenticates a target comprising: outputting a plurality of candidate responses to questions to the target on a display device; specifying a response to the question from among the candidate responses based on a target&#39;s gaze in a face image captured by an imaging device that captures a face image of the target; making a correctness or incorrectness judgment of the specified response; performing target&#39;s face authentication from the face image captured by the imaging device; performing target&#39;s biometrics determination based on changes in the target&#39;s gaze detected from a plurality of the face image; and authenticating the target based on results of the correctness or incorrectness judgment, the biometrics determination, and the face authentication. 
     (Supplementary note 9) The authentication method according to Supplementary note 8, further comprising: obtaining response time at which the target specified the response; obtaining a result of the face authentication performed at the same time as the response time; and authenticating that the target is a living body matched by the face authentication. 
     (Supplementary note 10) A program recording medium that stores an authentication program that is applied to a computer that authenticates a target, and causing the computer to execute: an output process of outputting a plurality of candidate responses to questions to the target on a display device; a response specification process of specifying a response to the question from among the candidate responses based on a target&#39;s gaze in a face image captured by an imaging device that captures a face image of the target; a response judgment process of making a correctness or incorrectness judgment of the specified response; a face authentication process of performing target&#39;s face authentication from the face image captured by the imaging device; a biometric determination process of performing target&#39;s biometrics determination based on changes in the target&#39;s gaze detected from a plurality of the face image; and a target authentication process of authenticating the target based on results of the correctness or incorrectness judgment, the biometrics determination, and the face authentication. 
     (Supplementary note 11) The program recording medium according to Supplementary note 10, wherein response time at which the target specified the response is obtained, in the response specification process, a result of the face authentication performed at the same time as the response time is obtained, in the face authentication process, and the target is authenticated as a living body matched by the face authentication, in the target authentication process. 
     (Supplementary note 12) An authentication program that is applied to a computer that authenticates a target, and causing the computer to execute: an output process of outputting a plurality of candidate responses to questions to the target on a display device; a response specification process of specifying a response to the question from among the candidate responses based on a target&#39;s gaze in a face image captured by an imaging device that captures a face image of the target; a response judgment process of making a correctness or incorrectness judgment of the specified response; a face authentication process of performing target&#39;s face authentication from the face image captured by the imaging device; a biometric determination process of performing target&#39;s biometrics determination based on changes in the target&#39;s gaze detected from a plurality of the face image; and a target authentication process of authenticating the target based on results of the correctness or incorrectness judgment, the biometrics determination, and the face authentication. 
     (Supplementary note 13) The authentication program according to Supplementary note 12, wherein response time at which the target specified the response is obtained, in the response specification process, a result of the face authentication performed at the same time as the response time is obtained, in the face authentication process, and the target is authenticated as a living body matched by the face authentication, in the target authentication process. 
     Although the invention of the present application has been described above with reference to example embodiment and the example, the present invention is not limited to the above example embodiment and the example. Various changes can be made to the configuration and details of the present invention that can be understood by those skilled in the art within the scope of the present invention. 
     INDUSTRIAL APPLICABILITY 
     The present invention is suitably applied to an authentication device that authenticates a target. Specifically, the invention can be used for personal authentication in financial transactions and contractual acts. Not only that, the invention can be applied to various industrial fields, such as the security field, such as restricting who can enter a certain area, or the commercial field, such as providing special services to a person visiting a certain store. 
     REFERENCE SIGNS LIST 
     
         
           10 ,  110 ,  210  Authentication device 
           11  Storage unit 
           12  Input unit 
           13  Output unit 
           14 ,  24  Response specification unit 
           15  Response judgment unit 
           16 ,  26  Face authentication unit 
           17 ,  37  Biometric determination unit 
           18 ,  28  Target authentication unit 
           20  Imaging device 
           30  Display device 
           100 ,  200 ,  300  Authentication system