Abstract:
A method of providing an image Completely Automatic Public Turing test to tell Computers and Humans Apart (CAPTCHA), and a server thereof. The method includes: outputting an image CAPTCHA including a plurality of images including a determination object image; receiving an image selection from the image CAPTCHA; determining whether a test of the image CAPTCHA is passed, based on the received image selection; and determining what the determination object image means. The images include a first group of images used to determine whether an accessing party passes the image CAPTCHA test and a second group of images unused to determine whether the accessing party passes the image CAPTCHA test. The second group includes the determination object image. The determining of the pass of the image CAPTCHA test is performed by selecting an image representing a correct or incorrect answer from the first group.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
       [0001]    A claim for priority under 35 U.S.C. §119 is made to Korean Patent Application No. 10-2015-0099369 filed Jul. 13, 2015, in the Korean Intellectual Property Office, the entire contents of which are hereby incorporated by reference. 
       BACKGROUND 
       [0002]    Statement of Technical Field 
         [0003]    The present disclosure relates to a method and a server for providing an image CAPTCHA. More particularly, the present disclosure relates to a method and a server for providing an image CAPTCHA which are capable of automatically determining a meaning of an image based on an image selection of an accessing party from the image CAPTCHA. 
       DESCRIPTION OF RELATED ART 
       [0004]    A CAPTCHA (Completely Automated Public Turing test to tell Computers and Humans Apart), which is an automated turing test, is made for the purpose of determining whether a currently accessing party is a human being. Malicious users sending e-mail spam attempt to secure a plurality of e-mail accounts by utilizing a robot automatically performing a predetermined work, but the CAPTCHA prevents such an attempt by generating tests that humans can pass but robots (or computer programs) cannot. The CAPTCHA is mainly utilized in web portal sites such as Google® and Bing® when confirming whether or not a user is human in a process of providing a resource such as an e-mail account. An image-based CAPTCHA introduced to improve problems of a character-based CAPTCHA mainly is a question of putting an interpretation on a meaning of an image, so that an ideal CAPTCHA may be implemented because there is a great difference between the image interpretation (recognition) abilities of human beings and robots. 
         [0005]    An image meaning determining and searching system (such as Google® image search or Bing® image search) according to the related art operates in such a manner that it searches for an image and a text from web pages and analyzes and conjectures the found text and image. However, even though a word is expressed in the same text, the word may have various meanings so that the meaning of the word may be ambiguous (for example, a phrase of ‘a true good scene’). In addition, since an image has several meanings, it may be difficult to express the image as a single text (for example, a phrase of ‘Baekdu-san mountain scene together with one&#39;s lover’). Further, when several photographs exist, it may be ambiguous to determine which photograph a text relates to. Thus, accuracy of a conventional scheme in which a text is analyzed to interpret an image is lower than that of a scheme in which human beings directly determines a meaning of an image. 
       SUMMARY 
       [0006]    The present disclosure concerns a method and a server for providing an image CAPTCHA, which provide the image CAPTCHA including an image unused to determine whether an accessing party is a human being and automatically determines what the image means based on the image selected by the accessing party, thereby making it possible to determine more exactly the meaning of an image at the minimum cost and by the minimum effort. 
         [0007]    The present disclosure also concerns a method of providing an image Completely Automatic Public Turing test to tell Computers and Humans Apart (CAPTCHA), which is performed by a server for providing an image CAPTCHA. The method includes: outputting an image CAPTCHA including a plurality of images including a determination object image; receiving an image selection from the image CAPTCHA; determining whether a test of the image CAPTCHA is passed, based on the received image selection; and determining what the determination object image means. The plurality of images includes a first group of images used to determine whether an accessing party passes the test of the image CAPTCHA. A second group of images are not used to determine whether the accessing party passes the test of the image CAPTCHA. The second group includes the determination object image. The determining of the test pass of the image CAPTCHA is performed by selecting an image representing a correct answer or an incorrect answer from the first group. 
         [0008]    The present disclosure further concerns a server for providing an image Completely Automatic Public Turing test to tell Computers and Humans Apart (CAPTCHA). The server includes: an interface unit configured to output an image CAPTCHA including a plurality of images including a determination object image and to receive an image selection from the output image CAPTCHA; and a control unit configured to determine whether an accessing party passes a test of the image CAPTCHA according to the received image selection and to determine what the determination object image means according to whether the accessing party passes the test. The plurality of images includes a first group of images used to determine whether the accessing party passes the test of the image CAPTCHA. A second group of images are not used to determine whether the accessing party passes the test of the image CAPTCHA. The determining of the test pass of the image CAPTCHA is performed by selecting an image from the first group. 
     
    
     
       BRIEF DESCRIPTION OF THE FIGURES 
         [0009]    The above and other objects and features will become apparent from the following description with reference to the following figures. 
           [0010]      FIG. 1  is a view illustrating a system for providing an image CAPTCHA. 
           [0011]      FIG. 2  is a block diagram illustrating a server for providing an image CAPTCHA. 
           [0012]      FIG. 3  is a flowchart illustrating a method of providing an image CAPTCHA to determine a meaning of a new image which is not determined. 
           [0013]      FIG. 4  is a flowchart illustrating a method of providing an image CAPTCHA to verify accuracy of a determination result. 
           [0014]      FIG. 5  is a view showing one example of an image CAPTCHA which is output to and displayed on an accessing party apparatus. 
           [0015]      FIG. 6  is a view illustrating a scheme of passing a test of an image CAPTCHA according to the related art. 
           [0016]      FIG. 7  is a view illustrating a scheme of passing a test of an image CAPTCHA. 
       
    
    
     DETAILED DESCRIPTION 
       [0017]    The objects, features and advantages of the disclosure will appear more fully upon consideration of the illustrative embodiments now to be described in detail with the accompanying drawings. Accordingly, the technological concepts of may be easily understood by one skilled in the art. It should be understood that the description herein will be given of essential parts required to understand operations according to this specification and description of the other parts will be omitted to obviate obscurity of the point of the invention. Hereinafter, embodiments will be described in detail with reference to accompanying drawings. 
         [0018]      FIG. 1  is a view illustrating a system for providing an image CAPTCHA. 
         [0019]    Referring to  FIG. 1 , a system for providing an image CAPTCHA includes at least one accessing party apparatus  200  and a server  100  for providing an image CAPTCHA. In some scenarios, the accessing party apparatus  200  and the image CAPTCHA providing server  100  may be connected to each other through Internet and may transmit and receive various kinds of data. 
         [0020]    Reviewing in brief each system block through one example of a system of providing an image CAPTCHA, the accessing party apparatus  200  may be connected to a server or other devices through Internet and may transmit/receive various kinds of data through Internet. For example, the accessing party apparatus  200  may include a personal computer, a mobile phone, a smart phone, a tablet PC, a specific-purpose server, etc. The accessing party apparatus  200  may access the image CAPTCHA providing server  100  to use a specific function provided from the server  100 . 
         [0021]    For example, the accessing party apparatus  200  may be an apparatus used to initially subscribe to the image CAPTCHA providing server  100  by a user or a robot trying to subscribe to the image CAPTCHA providing server  100  through a program installed thereto in order to maliciously utilize a function of the image CAPTCHA providing server  100 . The malicious robot is programmed to obtain a plurality of accounts by analyzing the images of image CAPTCHAs through a test wasting attack. 
         [0022]    The image CAPTCHA providing server  100  provides a server-purpose function to a subscribed or registered user. For example, the image CAPTCHA providing server  100  may be an e-mail server, a portal server, or a cloud server. The image CAPTCHA providing server  100  is configured to output an image CAPTCHA and determine whether the accessing party apparatus  200  is a human being, based on the selection from the images of the output image CAPTCHA. When a user passes the image CAPTCHA test, the image CAPTCHA providing server  100  may provide an account and a specific function or service to the user. In addition, the image CAPTCHA providing server  100  may analyze information about the image selection and the test pass to determine the meaning of the image. In this case, the image CAPTCHA providing system  100  may further include a separated image determination apparatus (not shown). The separated image determination apparatus may include a reception unit configured to receive the information about the selection and test pass of the accessing party apparatus  200  for the image to be determined by the image CAPTCHA server  100 , and a determination unit configured to determine the meaning of the image to be determined by analyzing the received information. 
         [0023]    The accessing party apparatus  200  and the image CAPTCHA providing server  100  may transmit various kinds of requests and response data through Internet according to the communication protocol of Internet protocol. The accessing party apparatus  200  transmits a request of securing an account to the image CAPTCHA providing server  100 , and the image CAPTCHA providing server  100  provides an image CAPTCHA including a plurality of images to the accessing party apparatus  200  in response to the request. As the image CAPTCHA server  100  receives the selection of the accessing party apparatus  200  from the provided image CAPTCHA and data or a response corresponding to the selection, the image CAPTCHA server  100  may determine whether the accessing party apparatus  200  passes the test and whether the user of the accessing party apparatus  200  is a human being, so that the image CAPTCHA providing server  100  provides an account to the accessing party apparatus  200  according to the determination result. 
         [0024]    The image CAPTCHA providing server  100  may variously interface with the accessing party apparatus  200 . For example, the image CAPTCHA providing server  100  may operate as a web server that provides a web page. The image CAPTCHA providing server  100  may be configured to transmit a web page to the accessing party apparatus  200  and receive data corresponding to the selection of the accessing party apparatus  200  from the images displayed on the web page. 
         [0025]    Hereinafter, an image CAPTCHA generated, a detailed control, and a data flow performed by utilizing the image CAPTCHA will be described in detail with reference to the accompanying drawings. 
         [0026]      FIG. 2  is a block diagram illustrating the image CAPTCHA server  100 . Referring to  FIG. 2 , the image CAPTCHA providing server  100  may include an interface unit  101 , a storage unit  103 , a control unit  105 , a connection unit  107  and additional other units.  FIG. 2  is a functional block diagram. 
         [0027]    Referring to  FIG. 2 , the interface unit  101  is connected to Internet to transmit/receive data to/from at least one accessing party apparatus  200 . For example, the interface unit  101  may transmit data corresponding to an image CAPTCHA to the accessing party apparatus  200  and may receive data corresponding to the selection of the accessing party apparatus  200  from the images included in the image CAPTCHA. To transmit/receive data, the interface unit  101  includes a chip set capable of performing wire local area communication such as Ethernet communication or wireless local area communication such as Wi-Fi communication. 
         [0028]    The storage unit  103  stores various kinds of data. The storage unit  103  includes at least one mass storage medium such as a volatile memory, a non-volatile memory or a hard disk. The storage unit  103  temporarily stores various kinds of data and programs by using a volatile memory and stores a system setting and a system program (such as a booting program) by using a non-volatile memory. The storage unit  103  stores various kinds of images, log data, and programs by using a mass storage medium such as a hard disk. 
         [0029]    The images stored in the storage unit  103  may be used to constitute or generate an image CAPTCHA. Although the images are collected at least through Internet, the images may be determined as correct or incorrect answers to specific questions or not yet. The programs stored in the storage unit  103  include a program for providing a server-purpose function, and a program for generating an image CAPTCHA and managing images and log data. For example, when an account is generated, a program related to the image CAPTCHA generation may be invoked such that an image CAPTCHA question is transmitted to the accessing party apparatus  200 . 
         [0030]    The control unit  105  controls each block of the image CAPTCHA providing server  100 . The control unit  105  includes an execution unit capable of executing a program code. In some scenarios, the control unit  105  loads the program code stored in the storage unit  103  to control each block according to the program. The control unit  105  includes at least one CPU or MPU. 
         [0031]    In this case, it is possible to allow a separated control unit to control a partial step (block). Control units may interwork with each other to control the image CAPTCHA server  100 . In detail, a step related to the image determination (for example, step S 111  of  FIG. 3  or steps S 211  to S 213  of  FIG. 4  described below) may be performed by a separated control unit. 
         [0032]    The control unit  105  may interwork with the interface unit  101  to transmit/receive various kinds of data to/from the accessing party apparatus  200 . The control unit  105  may be configured to perform a function assigned to the image CAPTCHA providing server  100  and perform a function corresponding to a request from the accessing party apparatus  200 . In this case, the control  105  is required to determine whether the accessing party apparatus  200  is a human being. For example, the control unit  105  generates an image CAPTCHA and outputs the image CAPTCHA through the interface unit  101  to determine whether the accessing party apparatus  200  is a human being. The control unit  105  receives the selection of the accessing party apparatus  200  from the image CAPTCHA through the interface unit  101  and determines whether the accessing party apparatus  200  is a human being according to the received selection such that a new account is provided to the accessing party apparatus  200  according to the determination result. 
         [0033]    A control process performed in the control unit  105  will be described in detail with reference to  FIGS. 3 and 4 . 
         [0034]    The connection unit  107  allows data to be transmitted/received between the blocks. The connection unit  107  is configured to transmit data of a block to the control unit  105  and transmit data generated from the control unit  105  to a block under control of the control unit  105 . For example, the connection unit  107  includes a parallel bus. 
         [0035]    The blocks of the image CAPTCHA providing server  100  of  FIG. 2  may be embedded in a single structure or be distributed into plural structures and embedded in them, respectively. In addition, the control unit  105  may be divided and embedded in plural structures. A form of the connection unit  107  may be changed according to the image CAPTCHA providing server  100 . 
         [0036]      FIG. 3  is a flowchart illustrating a method of providing an image CAPTCHA to determine a meaning of a new image which is not determined. The control flow of  FIG. 3  is performed by the image CAPTCHA providing server  100 . In some scenarios, the control unit  105  of the image CAPTCHA providing server  100  loads a program stored in the storage unit  103  to control the interface unit  101  and the storage unit  103  according to the program code such that the control unit  105  performs the control process. The control and data flows between the interworking blocks will be described in detail below. 
         [0037]    First, in step S 101 , the control unit  105  of the image CAPTCHA providing server  100  periodically collects new images through on-line or off-line and stores the collected images in the storage unit  103 . The step S 101  may be performed independently from other steps. 
         [0038]    In step S 103 , the control unit  105  of the image CAPTCHA providing server  100  configures an image CAPTCHA according to a request (for example, a request of generating an account) of the accessing party apparatus  200  through the interface unit  101 . The image CAPTCHA includes a plurality of images and a question which is a reference for selecting the images. 
         [0039]    First, the images of the image CAPTCHA, which all are correct or incorrect answer images, are configured to be unable to recognize identification. In detail, the image CAPTCHA includes a group (hereinafter, referred to as a ‘first group’) of images used to determine whether the accessing party passes the test and a group (hereinafter, referred to as a ‘second group’) of images unused to determine whether the accessing party passes the test. Hereinafter, an image of the second group will be referred to as a ‘neutral image’. 
         [0040]    An image of the first group is a correct or incorrect answer image previously classified. Differently from the image CAPTCHAs known in the art, since the image CAPTCHA includes all the images of the first and second groups, even when passing the test, the identifications of each image may be hidden. An image (neutral image) of the second group may be a correct or incorrect answer image previously classified or a new image not classified. The neutral image of the image CAPTCHA does not serve as the identification of a correct or incorrect answer. Thus, even though the accessing party apparatus  200  passes the image CAPTCHA test, it is impossible to determine correct or incorrect answer identifications of each image due to the neutral image. Since the test pass is determined by some (the image of the first group) of the images without regard to whether a neutral image is selected, it is impossible to verify the identifications of the images so that a test wasting attack may be prevented. 
         [0041]    That is, since the image CAPTCHA includes the neutral image, even though the accessing party apparatus  200  selects the incorrect answer image from the neutral images, the accessing party apparatus  200  may pass the test. After a robot mistakes the neutral image for an correct or incorrect answer, the robot may do the same selection for the corresponding image (although the image is a neutral image before, but the image may be selected as an image of the first group) in future, so that the image is utilized as a resource for protecting the robot. 
         [0042]    The neutral image disturbs an attempt to infer the identification of an image. Since it does not exert an influence on the result whether the neutral image is selected, the neutral image is utilized to determine identification of an image which is newly collected and will be described below. 
         [0043]    The image CAPTCHA includes at least one test image which is desired to determine the image and designated as a neutral image. The test image is an image which is not interpreted yet, that is, is desired to determine the meaning among images, the meanings of which are not determined. The test image may be a new image collected through on-line or off-line (See step S 101 ). 
         [0044]    After configuring the image CAPTCHA, in step S 105 , the control unit  105  of the image CAPTCHA providing server  100  outputs the image CAPTCHA to the accessing party apparatus  200  through the interface unit  101 . The output image CAPTCHA includes a question and a plurality of images which include the image(s) of the first group and the image(s) of the second group (neutral) including at least one test image. 
         [0045]      FIG. 5  is a view showing one example of an image CAPTCHA which is output to and displayed on the accessing party apparatus  200 . As shown in  FIG. 5 , the accessing party apparatus  200  receives the image CAPTCHA through Internet and displays the received image CAPTCHA thereon. A user or robot of the accessing party apparatus  200  selects a plurality of images included in the image CAPTCHA according to the question and transmits the data corresponding to the image selection to the image CAPTCHA providing server  100  through Internet. 
         [0046]    The control unit  105  of the image CAPTCHA providing server  100  receives the data corresponding to the image selection from the accessing party apparatus  200  through the interface unit  101  in step S 107 , and determines whether the accessing party apparatus  100  passes the image CAPTCHA test based on the received image selection (image selection from the first group) in step S 109 . The images used to determine the test pass are limited to the images of the first group. Without regard to whether the selection from the images of the second group is a correct or incorrect answer, the test pass is determined by selecting a correct or incorrect answer from the images of the first group. As the determination result, the control unit  105  approves or rejects the request (for example, of generating a new account) of the accessing party apparatus  200 . 
         [0047]    In addition, the control unit  105  stores the data representing the image selection and whether the test is passed in the storage unit  103  as log data. The data stored as the log data may include data on the question, identifiers of images, whether each image of the identifiers is selected, the number of selections of each image, the number of non-selection of each image, the number of CAPTCHAs including each image, whether an image is included in the first or second group, or whether an image CAPTCHA test is passed. The data on whether the test is passed may be stored corresponding to each image CAPTCHA output and thus, the probability of the test pass may be stored as log data. 
         [0048]      FIG. 6  is a view illustrating a scheme of passing a test of an image CAPTCHA according to the related art.  FIG. 7  is a view illustrating a scheme of passing a test of an image CAPTCHA. 
         [0049]    As shown in  FIG. 6 , according to a scheme of passing a test of an image CAPTCHA well known in the related art, if all correct answer images are selected and any incorrect answer images are not selected, the test is passed. When the accessing party apparatus  200  passes the test, all the identifications of the output images are exposed to the accessing party apparatus  200 . 
         [0050]    To the contrary, as shown in  FIG. 7 , the first group images are used to determine whether the test is passed through the selection of a correct or incorrect answer, and the second group (neutral) images including at least one test image are not used to determine whether the test is passed. Thus, even when a neutral image is incorrectly selected, the accessing party apparatus  200  may pass the test so that it is impossible to expose the identifications of the images as the test pass result. 
         [0051]    If the image CAPTCHA test is passed, the control unit  105  of the image CAPTCHA providing server  100  determines the test image in step S 111 . Only the log data on the test pass are used to determine the meaning of the test image. In case of a test pass, since the accessing party apparatus  200  is a human being or the possibility is great, the meaning of the corresponding question of the corresponding image may be determined as the selection of the accessing party apparatus  200 , which passes the test, for the correct or incorrect answer of the corresponding test image is received. For example, when the accessing party apparatus  200  passes a test of requesting to select a person ‘Bill Gates’ by selecting a correct test image(s) as the correct answer, the possibility that the test image(s) are ‘Bill Gates’ is great. 
         [0052]    In step S 111 , the meaning of the test image may be determined by selecting the test image several times. That is, when the sufficient log data are stored in the storage unit  103 , the control unit  105  may finally determine the meaning (correct or incorrect answer) of the test image by utilizing the log data. In detail, the control unit  105  repeatedly performs the steps S 103  to S 109  such that the control unit  105  collects a plurality of data representing whether the accessing party apparatus  200  passing the test selects the test image. When the collected data on the selection maintain a predetermined degree of homogeneity, the control unit  105  may determine the meaning of the test image based on the collected data in step S 111 . 
         [0053]    For example, when the accessing party apparatus  200  passes the image CAPTCHA test and the probability (the number of selecting a corresponding test image after passing the test/the number of performing the image CAPTCHA including the corresponding test image and passing the test) of selecting the test images of the second group as a correct answer is higher than a predetermined first determination reference probability (for example, 80%), the control unit  105  determines the meaning of the corresponding test image as a correct answer image of the corresponding question. 
         [0054]    In addition, after the accessing party apparatus  200  passes the image CAPTCHA test, when the probability of selecting a test image as a correct answer is less than a predetermined second determination reference probability (for example, 20%), the control unit  105  determines the meaning of the corresponding test image as an incorrect answer of the corresponding question. 
         [0055]    After the accessing party apparatus  200  passes a test, when the probability of selecting a test image as a correct answer is less than the first determination reference probability and is greater than the second determination reference probability, the control unit  105  defers determining the meaning of a correct or incorrect answer. In this case, the control unit  105  disposes the corresponding image as a test image again and repeatedly performs steps S 103  to S 109  and S 111 , such that the control unit  105  may collect data on the selection of the corresponding image and determine the meaning. When the number of the determinations of the test image of step S 111  exceeds a predetermined reference number and the test image is not determined as a correct or incorrect answer image, the control unit  105  may stop allowing the corresponding test image to be included in an image CAPTCHA question and remove the corresponding image. For example, when the reference number is set as ‘1’, and, as the result of performing the image determining step once, it is difficult to determine whether the answer is correct or incorrect, the control unit  105  may delete the corresponding test image. The reference number may be preset by an administrator. 
         [0056]    Differently from the scenario described above, the first determination reference probability may be equal to the second determination reference probability. In this case, when the probability of selecting a test image is greater than the first (or second) determination reference probability, the control unit  105  determines the test image as the correct answer. In addition, when the probability of selecting a test image is less than the first (or second) determination reference probability, the control unit  105  determines the test image as an incorrect answer. 
         [0057]    That is, to increase the accuracy of the image determination, the control unit  105  may determine the meaning of at least one test image desired to be determined based on plural selections from the accessing party apparatus  200  which has passed the test several times. 
         [0058]    Thus, the control unit  105  may determine the meaning of a new image, which is not automatically determined without intervention of a human being, by using the neutral image including the test image. In addition, since the accessing party (determined as a human being), which passes the test through an image CAPTCHA, is directly asked a question about whether the meaning proposed through the corresponding image is correct and the answer is received, as compared with a scheme of determining a meaning of a text-based image according to the related art, the possibility that an error occurs may be reduced and the meaning of an image may be more exactly determined. In addition, the determined meaning may be used to configure an image CAPTCHA in future. 
         [0059]    As described above, the steps S 103  to  109  are repeated and the storage unit  103  continuously stores the log data from several accessing party apparatus  200  therein. In this case, the images of the image CAPTCHA output through the steps S 103  to S 105  may be different from those of a previous image CAPTCHA. In addition, the first group images of a previous image CAPTCHA may be output as a neutral image in future. To the contrary, the neutral image may be output as an image of the first group in future. 
         [0060]    Differently from the scenario, the step S 111  of determining a test image may be performed by a separated image determination apparatus. In detail, the reception unit of the image determination apparatus receives information about the test image selection and the test pass from the image CAPTCHA providing server  100 , which is stored according to the result of performing the steps S 103  to S 109 , and the determination unit of the determination apparatus determines the meaning of the test image by using the received information. 
         [0061]      FIG. 4  is a flowchart illustrating a method of providing an image CAPTCHA to verify accuracy of the meaning determined in  FIG. 3 . The control flow of  FIG. 4  is performed by the image CAPTCHA providing server  100 . In some scenarios, the control unit  105  of the image CAPTCHA providing server  100  loads a program stored in the storage unit  103  and controls the interface unit  101  and the storage unit  103  according to the code of the program such that the control flow is performed. In this case, control and data flows interworking with each block will be described in detail. In following description about the control flow of  FIG. 4 , the same parts as those described above will be in brief described. 
         [0062]    First, the control unit  105  selects at least one verification object image desired to verify the accuracy of the determined meaning. In this case, the verification object image includes the image of which the meaning is determined through the process of  FIG. 3 . Differently from the scenario, it is possible to select, as the verification object image, the image of which the meaning is determined through another scheme. 
         [0063]    The control unit  105  may automatically select the verification object image according to a predetermined reference. The control unit  105  may select another image as the verification object image according to the predetermined reference, where the predetermined reference may be arbitrarily set by an administrator. 
         [0064]    For example, the predetermined reference may be the probability selected by a correct or incorrect answer. In detail, an image determined as a correct answer of a specific question is provided to an image CAPTCHA and an image, of which the probability (the selected number of the corresponding image as a correct answer/the performed number of CAPTCHA) that the image is selected as a correct answer is less than a predetermined first verification object selection reference probability (for example, 80%), may be selected as the verification object image. Alternatively, an image, of which the probability that the image is not selected as a correct answer (or incorrect answer) is greater than a predetermined second verification object selection reference probability (for example, 20%), may be selected. 
         [0065]    Likewise, an image determined as an incorrect answer of a specific question is provided to an image CAPTCHA and an image, of which the probability that the image is selected as an incorrect answer (or is not selected as a correct answer) is less than a predetermined third verification object selection reference probability (for example, 80%), may be selected as the verification object image. 
         [0066]    In addition, the predetermined reference may be a predetermined time period (for example, 30 days) after the meaning of the corresponding image is determined and the image may be selected as a verification object image after the predetermined time period is elapsed. Alternatively, it is possible to set, as the predetermined reference, the number of questions about the corresponding image included in an image CAPTCHA, that is, the number of questions about the corresponding image which is applied to an image CAPTCHA while being included in the first group as the identification of a correct (or incorrect) answer. When the number of questions of the corresponding image exceeds a predetermined number (for example, 100 times), the corresponding image may be selected as the verification object image. 
         [0067]    An administrator may arbitrarily select a verification object image. 
         [0068]    In step S 203 , the control unit  105  configures an image CAPTCHA including a verification object image (the meaning of which is determined through  FIG. 3 ) according to a request of generating an account from the accessing party apparatus  200  through the interface unit  101 . 
         [0069]    The configured image CAPTCHA includes an image of the first group used to determine the test pass and an image of the second group (neutral). At least one verification object image for verifying the accuracy of the determined meaning is included in the image CAPTCHA and is disposed as a neutral image. 
         [0070]    In step S 205 , the control unit  105  outputs the image CAPTCHA including images and a question to the accessing party apparatus  200  through the interface unit  101 . 
         [0071]    In step S 207 , the control unit  105  receives data representing an image selection from the accessing party apparatus  200  through the interface unit  101 . The received data representing an image selection are stored in the storage unit  103  as control log data of the control unit  105 . 
         [0072]    Then, in step S 209 , the control unit  105  determines whether the image CAPTCHA test is passed based on the received image selection (the selection of an image form the first group). The images used to determine whether the test is passed are limited to those in the first group. As the result of the test pass in step S 209 , the control unit  105  may generate a new account and informs the accessing party apparatus  200  of the generated account through the interface unit  101 . 
         [0073]    When the accessing party apparatus  200  passes the image CAPTCHA test, the control unit  105  determines the verification object image in step S 211 . To increase the accuracy of the image determination, the control unit  105  may determine the meaning of the verification object image based on plural selections from the accessing party apparatus  200  which has passed the test several times. 
         [0074]    Next, in step S 213 , the control unit  105  compares the meaning determined through step S 211  with the previous meaning (which is determined through step S 111  of  FIG. 3 ) of the verification object image such that the control unit  105  determines whether the meanings conflict with each other. In detail, when the verification object image meaning a correct (incorrect) answer of a specific question has the same meaning, it is determined that there is no conflict between the meanings. When it is determined that the verification object image has a different meaning, it is determined that inflict occurs between the meanings of the image. 
         [0075]    In this case, the control unit  105  may determine whether conflict occurs based on the result of determining an image several times in step S 211 . In some scenarios, when the verification object image is determined based on the selection once in step S 211 , the control unit  104  may determine whether conflict occurs based on plural determination results in step S 213 . That is, when the accessing object apparatus  200  passes the image CAPTCHA test, the control unit  105  determines at least one verification object image as a correct or incorrect answer image based on the selection of the accessing object apparatus  200  in step S 211 . When plural determination results collected by repeating steps S 203  to S 211  maintain a predetermined degree of homogeneity, based on it, the control unit  105  may determine whether the determination results conflict with the previous determination result of the verification object image or the previous identification in step S 213 . 
         [0076]    For example, when the accessing party apparatus  200  passes the image CAPTCHA test and the probability that the verification object image meaning a correct (incorrect) answer of a specific question is determined as an incorrect (correct) answer in step S 211  is less than a predetermined first conflict reference probability (for example, 20%), the control unit  105  determines that conflict does not occur. 
         [0077]    In addition, when the probability that the verification object image meaning a correct (incorrect) answer of a specific question is determined as an incorrect (correct) answer is greater than the first conflict reference probability, the control unit  105  determines that conflict occurs. In this case, only when the probability that the verification object image meaning a correct (incorrect) answer is determined as an incorrect (correct) answer is less than a second conflict reference probability (for example, 80%), the control unit  105  determines that conflict occurs. When the probability that the verification object image meaning a correct (incorrect) answer is determined as an incorrect (correct) answer is greater than the first conflict reference probability and less than the second conflict reference probability, the control unit  105  may defer determining whether conflict occurs. 
         [0078]    When the control unit  105  may defer determining whether conflict occurs, the control unit  105  disposes the corresponding image as a verification object image again and repeats steps S 203  to S 211 , such that the control unit  105  may determine the meaning of the corresponding image again and may determine whether the meaning of the corresponding image conflicts with the previous determination result again. When the number of the conflict determinations of step S 213  exceeds a predetermined reference number and it is not determined whether the conflict of the verification object image occurs, the control unit  105  may stop to allow the verification object image to be included in an image CAPTCHA question and remove the corresponding image. For example, when the reference number is set as ‘1’, and, as the result of performing the image conflict determining step of step S 213  once, if it is difficult to determine whether conflict occurs or not, the control unit  105  may delete the corresponding verification object image. The reference number may be preset by an administrator. 
         [0079]    Lastly, in steps S 215  and S 216 , the control unit  105  may remove, reuse or revalue the verification object image according to whether conflict occurs. That is, when any conflict does not occur, the determination result of the corresponding image is maintained as it is and reuses the corresponding image for an image CAPTCHA base on the determined meaning. 
         [0080]    When conflict occurs, the corresponding verification object image may be removed. Alternatively, when conflict occurs, it is possible to revalue the corresponding verification object image after removing the determined meaning of the corresponding verification object image. For example, after removing the determined meaning of the corresponding verification object image, the image having no determined meaning may be stored as a test image of  FIG. 3 , and the meaning may be determined according to a scheme of providing an image CAPTCHA of  FIG. 3 . 
         [0081]    That is, to increase the accuracy of the image determination result verification, the control unit  105  may determine the meaning of the verification object image based on plural selections from the accessing party apparatus  200  which has passed the test several times. In addition, the control unit  105  may determine whether the meaning of the verification object image conflicts with the previous determination result. As the result, the control unit  105  may remove, reuse or revalue the corresponding image. 
         [0082]    The steps S 203  to S 216  may be repeated according to the request of the accessing party apparatus  200  and as repeated, the storage unit  103  continuously stores the log data from several accessing party apparatus  200  therein. 
         [0083]    Thus, the control unit  105  may determine the meaning of the determined image without intervention of a human being, and may suitably apply the meaning which is changed as time is elapsed or the condition is changed by repeating the verification. 
         [0084]    Differently from the scenario, the step S 211  of determining a test image may be performed by a separated image determination apparatus. In detail, the reception unit of the image determination apparatus receives information about the verification object image selection and the test pass from the image CAPTCHA providing server  100 , which is stored according to the result of performing the steps S 203  to S 209 , and the determination unit of the determination apparatus determines the meaning of the verification object image by using the received information. In addition, the step S 213  of determining whether the conflict of the verification object image occurs may be performed by the image determination apparatus. 
         [0085]    According to the image CAPTCHA, the image desired to determine the meaning is disposed as a neutral image, so that the meaning of the image may be automatically determined based on whether the accessing party (human being) which has passed the test selects the image desired to determine the meaning. In addition, according to the image CAPTCHA, the meaning determined image is disposed as a neutral image such that the meaning of the image is determined again and the meaning conflicts with a previous determined meaning, so that the accuracy of the image determination may be improved. Further, even when the test including the image CAPTCHA is passed, it is impossible to expose the identifications of the each image. 
         [0086]    According to the method and server for providing an image CAPTCHA, the meaning of an image may be exactly determined and the determined image may be verified by using the image CAPTCHA including a neutral image without intervention of a human being. 
         [0087]    While the inventive concept has been described with reference to embodiments, it will be apparent to those skilled in the art that various changes and modifications may be made without departing from the spirit and scope of the inventive concept. Therefore, it should be understood that the above embodiments are not limiting, but illustrative.