KR101138551B1 - System and method for providing captcha - Google Patents

Abstract

CAPTCHA (Complete Automated Public Turing Test To Tell Computers and Human Apart) providing systems and methods are provided. The captcha providing system according to an embodiment of the present invention generates and provides a fusion captcha of text and an image. In addition, the captcha providing system according to another embodiment of the present invention generates and provides a composite image captcha by combining a plurality of images.

Description

CAPTCHA SYSTEM AND METHOD {SYSTEM AND METHOD FOR PROVIDING CAPTCHA}

System and method for providing a CAPTCHA (Complete Automated Public Turing Test To Tell Computers and Human Apart), and more specifically, a system for collecting keywords or images used to generate CAPTCHA and generating and providing them as CAPTCHA; It is related to the method.

In the application and use of web services on the Internet, automated programs can access and illegally collect large amounts of information, distort the results of Internet surveys, and cause unnecessary communication and data processing.

In order to solve this problem, the concept of security function introduced by Luis von Ahn in 2000 is CAPTCHA (Complete Automated Public Turing Test To Tell Computers and Human Apart).

The Captcha system is difficult to solve with current automated software technology, but automatically generates and solves problems that human users can easily solve (hereinafter referred to as 'Capcha'), thereby preventing access to automated programs. And only the actual human user can access the service.

These capchas are expanding their applications such as membership registration on the website, online survey certification, and certification when participating in the auction of portal sites.

Meanwhile, in the related art, text is provided in the form of an image in a deformed form and a text-based captcha for allowing the user to fit the text, or one or more images, and the user is allowed to fit the text corresponding to the image. Image-based Captcha has been proposed.

However, with the development of OCR (Optical Character Recognition) technology, the problem of text-based Captcha being recognized by the bot program is found, and the image-based Captcha is corrected by the human user inputting an incorrect There was a falling inefficiency.

Embodiments of the present invention provide a system and method for providing a CAPTCHA that has a high correct answer rate to a user who is human and improves user convenience.

Embodiments of the present invention provide a highly reliable CAPTCHA providing system and method that is not analyzed by an automated program by iterative machine learning.

In addition, embodiments of the present invention provides a system and method for providing a CAPTCHA that can reduce storage space overhead or transmission overhead by reducing the number of images required when using an image for CAPTCHA.

According to an aspect of the present invention, by using a keyword selecting unit for selecting a keyword from a database, an image selecting unit for selecting at least one image corresponding to the selected keyword from the database, and using the keyword and the at least one image A captcha providing system including a captcha generating unit for generating a captcha is provided.

Here, the keyword selecting unit may randomly select the keyword from the database.

The image selecting unit may randomly select at least one image corresponding to the selected keyword among images stored in the database.

The captcha generation unit may generate the captcha by fusing the keyword modified image modified with the keyword and the at least one image.

According to an embodiment of the present invention, the captcha providing system further includes an image collecting unit collecting additional images for adding to the database, and a filter unit filtering and storing the collected additional images in the database.

According to another aspect of the present invention, there is provided a captcha providing system including an image selecting unit for selecting a plurality of images from a database, and a captcha generating unit for generating a captcha by combining the plurality of images.

Here, the captcha generation unit may generate a captcha by extracting some pixels from each of the plurality of images and combining one image.

According to an embodiment of the present invention, the captcha generation unit further generates event information for reconstructing each of the plurality of images from the captcha.

In this case, the event information is to extract the first image by using odd-numbered column pixels of the odd-numbered row of the captcha, and to extract the second image by using even-numbered column pixels of the even-numbered row of the captcha. Can be.

According to an embodiment of the present invention, the captcha generation unit includes at least a portion of at least one keyword corresponding to each of at least one of the plurality of images in the captcha.

According to another aspect of the present invention, a keyword selecting step of selecting a keyword from a database, an image selecting step of selecting at least one image corresponding to the selected keyword from the database, and the keyword and the at least one image There is provided a captcha providing method comprising a captcha generating step of generating a captcha using the captcha.

According to still another aspect of the present invention, there is provided a captcha providing method comprising an image selecting step of selecting a plurality of images from a database, and a captcha generating step of combining the plurality of images to generate a captcha.

According to embodiments of the present invention, there is provided a system and method for providing a CAPTCHA that has high user convenience and high reliability, and has a high answer rate by a human user and is not analyzed by an automated program.

In addition, according to embodiments of the present invention, when the image is used in the CAPTCHA, by reducing the number of images required to reduce the storage overhead or transmission overhead to improve the CAPTCHA system operating efficiency.

1 illustrates a CAPTCHA providing system according to an embodiment of the present invention.
2 is a conceptual diagram illustrating a relationship between a keyword and an image stored in a database according to an embodiment of the present invention.
3 illustrates a fusion captcha of text and images generated in accordance with one embodiment of the present invention.
4 is a conceptual diagram illustrating a process of generating one composite image captcha from a plurality of images according to an embodiment of the present invention.
5 illustrates a composite image captcha generated through the process of FIG. 4, according to an embodiment of the present invention.
6 is a conceptual diagram illustrating a process of restoring a plurality of images from a composite image captcha by a client receiving the composite image captcha of FIG. 5 according to one embodiment of the present invention.
7 is a flowchart illustrating a process of generating a fusion captcha of text and an image by a captcha providing method according to an exemplary embodiment of the present invention.
8 is a flowchart illustrating a process of generating a composite image captcha by a captcha providing method according to an exemplary embodiment of the present invention.
9 is a flowchart illustrating an image collection and filtering process for further storing an image in a database according to an embodiment of the present invention.

Hereinafter, some embodiments of the present invention will be described in detail with reference to the accompanying drawings. However, the present invention is not limited or limited by the embodiments. Like reference numerals in the drawings denote like elements.

1 illustrates a CAPTCHA providing system 100 according to an embodiment of the present invention.

The captcha providing system 100 may include an image collecting unit 101, a filter unit 102, a database 110, a keyword selecting unit 120, an image selecting unit 130, and a captcha generating unit 140. .

According to an embodiment of the present invention, when a captcha provision request is received at the captcha provision system 100, a fusion captcha of text and image may be generated.

In this case, the keyword selecting unit 120 of the CAPTCHA providing system 100 selects at least one keyword from the database 110. This selection may be made randomly or may be made by other constant methods.

Then, the image selecting unit 130 of the captcha providing system 100 selects at least one image corresponding to each of the at least one keyword from the database 110. Such image selection may also be made randomly.

When the keyword and the image corresponding to the keyword is selected, the captcha generation unit 140 of the captcha providing system 100 generates a fusion captcha of the text and the image. The meaning of the fusion captcha of the text and image and a process of generating the same will be described later in more detail with reference to FIGS. 2 to 3.

According to another embodiment of the present invention, when a captcha provision request is received, the captcha provision system 100 generates and provides a composite image captcha.

The image selecting unit 130 of the captcha providing system 100 selects a plurality of images from the database 110. The selection of such images may also be made randomly or by some other constant method.

Then, the captcha generation unit 140 combines the selected plurality of images to generate a composite image captcha, and provides the generated captcha and event information corresponding to the restored information of the combined captcha.

More detailed information about the composite image captcha, the meaning of the event information, and a generating method thereof will be described later with reference to FIGS. 2 and 4 to 6.

Meanwhile, the construction of the database 110 by matching and storing keywords and images may be performed by the image collector 101 and the filter 102. The image collecting unit 101 collects images from an external DB, and the filter unit 102 filters the images and stores only the images having a high relation with the keywords in the database 110.

Here, the filter unit 102 may filter the images collected by the image collecting unit 101 by using one or more types of different filtering methods.

For example, in the first filtering, text-based filtering is performed by using meta information of an image (for example, a file name, etc.) by contrast with a keyword to filter out an image that is less related to a keyword, and in the second filtering. Embodiments such as filtering out an image having low association with the keyword once again through color based filtering are possible.

For example, in response to the keyword "strawberry", an image having a high ratio of completely different colors may be filtered out through the red filter in the second filtering.

The database construction by the operation of the image collecting unit 101 and the filter unit 102 will be described later in more detail with reference to FIG. 9.

2 is a conceptual diagram illustrating a relationship between a keyword and an image stored in the database 110 according to an embodiment of the present invention.

According to an embodiment of the present invention, a plurality of keywords 210 and a plurality of images 220 are stored in the database 110. In this case, each of the keywords 210 is associated and stored to match at least one image.

For example, the keyword "211" as a "car" is stored in association with an image 221 and an image 222 that may associate a car with a user. The keyword 212, "apple," is stored in association with the image 223 and the image 224, which may be associated with an apple to a user who is a person.

In this case, unlike the above-described embodiment, an embodiment in which one keyword corresponds to one image is possible, and in contrast, another embodiment in which a plurality of keywords corresponds to one image is possible. In addition, some of the keywords may be matched to only one image, and some of the other keywords may be associated and stored to match one or more images.

Therefore, the matching relationship between each of the keywords 210 and the images 220 stored in the database 110 may be set in various ways without departing from the spirit of the present invention, and the present invention is limited by some embodiments. It should not be interpreted as

As described above, in the conventional text-based CAPTCHA providing system, an image modified from a keyword is provided so that a user who is a person matches the keyword. In the image-based CAPTCHA providing system, only the image is provided and a user who matches a keyword corresponding to the provided image is adjusted.

However, in the case of a text-based Captcha providing system, there are many cases in which a keyword is identified and recognized by an automated program such as a bot program according to the development of OCR technology, and thus the reliability is not high.

In addition, in the image-based CAPTCHA, a user who is a human may input other keywords that may be associated with the correct answer keyword through the provided image, which may cause problems in user convenience.

For example, in the case where the image 221 is provided as a Captcha, a person fails to match the keyword "car", which is the correct answer, and enters another keyword that is incorrect. For example, a user who is a human is provided with an image 221 as a cap car, and inputs "car", "car", "sedan", "private", or a specific car model ("Benz", "S500", etc.).

This low answer rate is not only a problem that the user is uncomfortable due to low user convenience, but also a problem of system load increase due to repeated captcha provision.

There have been attempts to recognize such a problem and provide a plurality of images together to improve reliability, but there are also problems of user convenience, and transmission overhead is often a problem by providing a plurality of images.

Therefore, according to an embodiment of the present invention, the captcha providing system 100 synthesizes the keyword and the modified image that is a hint (Tip) to match the keyword corresponding to the image with the user, one captcha Provided as. This is also referred to as "fusion captcha of text and image", which will be described below in more detail with reference to FIG. 3.

Meanwhile, according to another embodiment of the present invention, the captcha providing system 100 provides one image, which is a combination of a plurality of images, as one captcha. This is also referred to as "composite image captcha", which will be described below in more detail with reference to FIGS. 4 to 6.

In addition, according to another embodiment of the present invention, the captcha providing system 100 synthesizes keywords corresponding to at least a part of a plurality of images synthesized in the composite image captcha together, and combines the above embodiments. Captcha may also be provided.

First, an embodiment of a fusion captcha of text and an image will be described with reference to FIG. 3.

3 illustrates a fusion captcha 300 of text and images generated in accordance with one embodiment of the present invention.

According to an embodiment of the present invention, the keyword selecting unit 120 of the CAPTCHA providing system 100 of FIG. 1 selects any one keyword 211 among the plurality of keywords 210 stored in the database 110. .

In this case, the keyword selection may be based on a method of randomly selecting among the keywords in the database 110.

Here, the keyword is randomly selected is only one embodiment of the present invention, it is apparent to those skilled in the art that according to another embodiment it may be by another extraction algorithm (for example, round robin). Accordingly, the present invention should not be construed as limited by some embodiments.

Then, the image selecting unit 130 of the captcha providing system 100 selects a plurality of images 221, 222, etc. of the images 220 stored in the database 110 that match the selected keyword 211. To identify.

The image selector 130 selects any one image 221 from among the plurality of images 221 and 222. Such image selection may also be made randomly.

Of course, it is only one embodiment of the present invention that the image selection is made randomly. According to another embodiment, it is possible to use a different extraction algorithm as described above.

On the other hand, if there is not one image but a plurality of images corresponding to the selected keyword, the image selecting unit 130 identifies the image corresponding to the selected keyword as a fusion cap of text and image. The image to be synthesized is selected.

In addition, in another embodiment of the present invention, the image selector 130 selects any one of the images 220 and then the keyword selector 120 identifies a keyword matching the selected image. It is possible. In the following, the present invention should not be limitedly interpreted by some embodiments with respect to the method or order of selecting keywords and / or images even if there is no mention.

Referring again to the exemplary embodiment of FIG. 3, the keyword “211” is selected by the keyword selector 120 and matches the keyword “211” by the image selector 130. An image 221 is selected among the images 221, 222, and the like.

Then, the captcha generation unit 140 generates the captcha 300 using the keyword 211 and the image 221.

Here, the image 221 is included as part 310 in the captcha 300, and the modified text images 320 and 330 corresponding to the keyword 211 are included as part in the captcha 300.

Here, as observed in the deformed text images 320 and 330, the captcha generation unit 140 does not let the user know all of the selected keyword “car”, but only a single letter which is a part of syllables of the keyword (captcha ( 300) Randomly placed in the image so that the user can understand it as a hint. The user may use the single image 320 and 330 included in the captcha 300 as a hint, so that all of the keywords (“car” in this example) or some of the keywords not included in the captcha 300 (“dragon” in this example) are included. Just type

On the other hand, in another embodiment of the present invention, it is also possible to process a portion of the keyword (in this example, "dragon") not included in the captcha 300 as blank.

In the above, the captcha 300 which is a fusion captcha of text and an image has been presented as an example, but in the process of synthesizing the modified image 320 of the image 310 and the keyword as a single captcha 300, It will be apparent to those skilled in the art that various modifications may be made without departing from the spirit, and such modifications are not excluded from the present invention.

For example, two or more keywords of the keywords 210 of the database 110 are selected, and images corresponding to each of these keywords are selected from the images 220, all together to fuse a text and image together. Can be generated as

Also in this case, modified images in which at least some syllables are blanked in each of these keywords may be included.

For example, when the image 221 and the image 224 are selected, the "dragon" in the "car" of the keyword 211 is treated as blank, and the "apple" in the "apple" of the keyword 212 as blank. Modified keyword images may be included and provided as one captcha.

Meanwhile, according to another embodiment of the present invention, the captcha providing system 100 may generate and provide a composite image captcha in addition to the fusion captcha of the text and the image.

In this case, in some embodiments, the captcha providing system 100 may generate only one type of captcha, either a fusion captcha of text and an image or a composite image captcha. Both types of fusion captcha and composite image captcha of the image can be generated, in which case one type of captcha can be provided at random.

In addition, an embodiment in which any one of the two types of capchas is provided first and an incorrect answer is input by the user may be provided.

4 is a conceptual diagram illustrating a process of generating one composite image captcha from a plurality of images according to an embodiment of the present invention.

In this embodiment, one composite image captcha is generated from two images.

The two selected images 410 and 420 are selected from the database 110 by the image selector 130 of the CAPTCHA providing system 100. In this process, the two images 410 and 420 may be selected randomly or by another algorithm among the images 220.

As in the present embodiment, when the two images are to be selected and synthesized, the captcha generation unit 140 may synthesize the image 410 and the image 420 in a grid pattern.

For example, the captcha generation unit 140, in the image 410, pixels 411 and 413 of odd columns among pixels 411, 412, 413, and 414 in odd rows. And even rows of pixels 412 and 414 may be removed.

In addition, among the pixels in the even row of the image 410, the pixels in the odd column may be removed while leaving the pixels in the even column, as opposed to the odd row. The shaded portion in FIG. 4 corresponds to the residual pixel.

Meanwhile, in the image 420, the captcha generation unit 140 leaves the even-numbered columns of pixels 422, 424, etc. among the odd-numbered rows of pixels 421, 422, 423, and 424. The pixels 421 and 423 may be removed.

In addition, among the pixels in the even row of the image 420, the pixels in the even column may be removed while leaving the pixels in the odd column, as opposed to the odd row. Again, residual pixels are shown shaded.

On the other hand, this method is only one embodiment of the present invention, it is apparent to those skilled in the art that various modifications are possible within the scope without departing from the spirit of the invention based on the description of these embodiments.

For example, some pixels may be removed in the same manner in both image 410 and image 420.

In another embodiment of the present invention, three or more images may be selected instead of two, and all of them may be synthesized together. In this case, if N images are selected, in the first image of N images, only the pixels having an index mod (N) = 1 (the pixels having the pixel index divided by N divided by N in the image) remain in the first image. Remove the pixels, remove the remaining pixels leaving only the pixels at index mod (N) = 2 in the second image, and remove the remaining pixels leaving only the pixels at index mod (N) = i in the i th image. It is possible.

Of course, this is also only one embodiment of the present invention, and various other methods for image compositing may be utilized.

Meanwhile, the images 220 of the database 110 may have different resolutions, and a method in which images of different resolutions are combined together is also possible.

In the following, various embodiments are not specifically mentioned, but a plurality of images may be obtained by extracting some pixels from each of the two or more images, synthesizing the extracted pixels in a predetermined pattern, and generating one composite image. Obviously, various methods that can reduce the transmission overhead compared to the case of transmitting all of them can be selected as an image composition method for the implementation of the present invention.

5 illustrates a composite image captcha generated through the process of FIG. 4, according to an embodiment of the present invention.

According to the embodiment of FIG. 4, which synthesizes two images 410 and 420, the captcha generator 140 generates the captcha 500 which is a composite image captcha.

In Captcha 500, some pixels 411, 413, etc. are pixels extracted from image 410, and some other pixels 422, 424, etc. are pixels extracted from image 420.

When the captcha generation unit 140 combines two or more images by a specific method and generates the composite image captcha, the captcha generation unit 140 identifies the specific method and extracts two images from the captcha at the client end again. Information that can be restored (hereinafter, referred to as "event information") is generated and provided together with the CAPTCHA 500.

Then, the client terminal may receive the event information together with the CAPTCHA 500, and extract each of the two images from the CAPTCHA 500 with reference to the event information. This process will be described later with reference to FIG. 6.

6 is a conceptual diagram illustrating a process of restoring a plurality of images from a composite image captcha by a client receiving the composite image captcha of FIG. 5 according to one embodiment of the present invention.

The CAPTCHA 500 and event information of FIG. 5 generated according to an embodiment of the present invention are received at the client end.

The client terminal extracts pixels 411 and 413 from the captcha 500 and interpolates the extracted pixels to pixels 611 and 612 with reference to the event information. Create a (restored image) 610.

In addition, with reference to the same event information, the client terminal extracts the pixels 422 and 424 from the captcha 500 and interpolates the extracted pixels to the pixels 621 and 622 to interpolate the second reconstructed image ( 620 is generated.

The method of interpolation may be various interpolations known in the field of image processing, such as linear interpolation.

Further, in another embodiment of the present invention, without such interpolation, a first reconstructed image is generated only by using the extracted pixels 411, 413, and the like, and only by using pixels 422, 424, and the like. The second reconstructed image may be generated.

And in another embodiment of the present invention, even such reconstruction image generation may be omitted. That is, in the synthesized image, if the user who is a human being can recognize each image, it is also possible that the capcha 500 itself is directly displayed to the user who is a human being.

7 is a flowchart illustrating a process of generating a fusion captcha of text and an image by a captcha providing method according to an exemplary embodiment of the present invention.

In step S710, a CAPTCHA provision request is received at the CAPTCHA provision system 100.

Then, in step S720, the keyword selecting unit 120 of the CAPTCHA providing system 100 selects at least one keyword from the database 110. As described above, such selection may be made randomly.

In operation S730, the image selecting unit 130 of the captcha providing system 100 selects at least one image corresponding to each of the at least one keyword from the database 110. Such image selection may also be made randomly.

Meanwhile, the order of keyword selection in step S720 and image selection in step S730 may be interchanged.

When the keyword and the image corresponding to the keyword is selected in this way, in step S740, the captcha generation unit 140 of the captcha providing system 100 generates a fusion captcha of the text and the image. This captcha generation process is as described above with reference to FIGS.

Then, in step S750, the captcha providing system 100 provides the fusion captcha of the generated text and image as a response to the captcha providing request.

8 is a flowchart illustrating a process of generating a composite image captcha by a captcha providing method according to an exemplary embodiment of the present invention.

In step S810, the CAPTCHA provision system 100 receives a CAPTCHA provision request.

Then, the image selecting unit 130 of the captcha providing system 100 selects a plurality of images from the database 110 in step S820. As described above, the selection of such an image may also be performed at random.

In operation S830, the captcha generation unit 140 combines the selected plurality of images to generate a composite image captcha, and corresponds to the restored information of the captcha synthesized with the captcha thus generated in step S840. Provide event information together.

The generation of the composite image captcha and the provision of event information are the same as described above with reference to FIGS. 1 to 2 and 4 to 6.

9 is a flowchart illustrating an image collection and filtering process for further storing an image in a database according to an embodiment of the present invention.

According to an embodiment of the present invention, the image collection unit 101 of the CAPTCHA providing system 100 transmits an image search query (Quarry) to an external web server, such as an open DB of a portal site, in step S910. .

This image search query corresponds to a pre-selected keyword.

When the search result images for the image search query are received in operation S920, the filter unit 102 of the CAPTCHA providing system 100 filters the received images to match the keyword in operation S930. Only some images are stored in the database 110.

Such filtering may include one or more kinds of different filtering processes as described above with reference to FIG. 1.

Specifically, in the first filtering, text-based filtering is performed by using the meta information of the image (for example, the file name, etc.) by contrast with the keyword, and the filter out the low correlation with the keyword. In the filtering, color-based filtering may be used to filter out an image having low association with the keyword once again.

For example, in response to the keyword "strawberry", an image having a high ratio of completely different colors may be filtered out through the red filter in the second filtering.

When the image finally remaining after the filtering is stored in the database 110 in operation S940, various embodiments of the method for providing a captcha of the present invention described with reference to the flowcharts of FIGS. 7 to 8 are performed.

The method according to an embodiment of the present invention can be implemented in the form of a program command which can be executed through various computer means and recorded in a computer-readable medium. The computer readable medium may include program instructions, data files, data structures, etc. alone or in combination. Program instructions recorded on the media may be those specially designed and constructed for the purposes of the present invention, or they may be of the kind well-known and available to those having skill in the computer software arts. Examples of computer-readable recording media include magnetic media such as hard disks, floppy disks, and magnetic tape, optical media such as CD-ROMs, DVDs, and magnetic disks, such as floppy disks. Magneto-optical media, and hardware systems specifically configured to store and execute program instructions, such as ROM, RAM, flash memory, and the like. Examples of program instructions include not only machine code generated by a compiler, but also high-level language code that can be executed by a computer using an interpreter or the like. The hardware system described above may be configured to operate as one or more software modules to perform the operations of the present invention, and vice versa.

As described above, the present invention has been described by way of limited embodiments and drawings, but the present invention is not limited to the above embodiments, and those skilled in the art to which the present invention pertains various modifications and variations from such descriptions. This is possible.

Therefore, the scope of the present invention should not be limited to the described embodiments, but should be determined not only by the claims below but also by the equivalents of the claims.

100: Captcha Delivery System
101: image collector
102: filter unit
110: Database
120: keyword selection unit
130: image selection unit
140: captcha generation unit

Claims (21)

delete delete delete delete delete delete An image selecting unit selecting a plurality of images from a database; And
Captcha generation unit for generating a captcha by combining the plurality of images
Including,
The captcha generating unit extracts some pixels from each of the plurality of images, and combines one image to generate the captcha. An image selecting unit selecting a plurality of images from a database; And
Captcha generation unit for generating a captcha by combining the plurality of images
Including,
The captcha generation unit further comprises event information for restoring each of the plurality of images from the captcha. The method of claim 8,
The event information may include extracting a first image by using odd-numbered column pixels of the odd-numbered row of the captcha, and extracting a second image by using even-numbered column pixels of the even-numbered row of the captcha. Captcha delivery system. The method according to any one of claims 7 to 8,
The cap tea generator,
And at least a portion of at least one keyword corresponding to each of at least one image of the plurality of images in the captcha. delete delete delete delete delete delete An image selecting step of selecting a plurality of images from a database of the captcha providing system by an image selecting unit of a captcha providing system; And
A captcha generation step of generating a captcha by combining the plurality of images by the captcha generation unit of the captcha providing system.
Including,
In the captcha generating step, a captcha providing method comprises extracting some pixels from each of the plurality of images and combining one image to generate a captcha. An image selecting step of selecting a plurality of images from a database of the captcha providing system by an image selecting unit of a captcha providing system; And
A captcha generation step of generating a captcha by combining the plurality of images by the captcha generation unit of the captcha providing system.
Including,
In the captcha generating step, the captcha providing method further comprises event information for reconstructing each of the plurality of images from the captcha. The method of claim 18,
The event information may include extracting a first image by using odd-numbered column pixels of the odd-numbered row of the captcha, and extracting a second image by using even-numbered column pixels of the even-numbered row of the captcha. How to provide Captcha. The method according to any one of claims 17 or 18,
The captcha generation step,
And at least a portion of at least one keyword corresponding to each of at least one image of the plurality of images in the captcha. A computer-readable recording medium in which a program for executing the method of any one of claims 17 to 19 is recorded.

Images