A SURVEY OF CURRENT RESEARCH ON CAPTCHA
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paper_title: Is it human or computer? Defending e-commerce with Captchas

paper_content:

A Captcha - a completely automatic public Turing test to tell computers and humans apart - is a test that humans can pass but computer programs cannot; such tests are becoming key to defending e-commerce systems. By using a Captcha, for example, IT systems can permit only real people-rather than a spammer's script-to create a free e-mail account. This article explains the various types of Captchas and discusses their strengths and weaknesses as a security measure. It also lists sources for more information on the formal research into Captchas.
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paper_title: A new architecture for the generation of picture based CAPTCHA

paper_content:

Automated network attack such as denial-of-service (DoS) leads to significant wastage of resources, which is a common threat to network security. To prevent these automated network attacks CAPTCHA based security mechanism is to be adopted so that it will differentiate humans from machines. Optical Character Recognition (OCR) based CAPTCHAs are more vulnerable to automated attacks due to the existence of correlation algorithms and direct distortion estimation techniques. The illegibility of the text CAPTCHA makes the user difficult to read it and thus they feel uncomfortable. In order to overcome these difficulties a new type of CAPTCHA, that is, picture based CAPTCHAs came into existence, which are more efficient and secure than the existing text based CAPTCHAs. We propose a new architecture for the generation of picture based CAPTCHA, which is resistant to segmentation through edge detection and thresholding, shape matching and random guessing. Our security analysis shows that the proposed architecture is showing better results in comparison with other picture based CAPTCHAs.
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paper_title: A 3-layer Dynamic CAPTCHA Implementation

paper_content:

In order to prevent the attack from malicious progroms,the server system introduces CAPTCHA mechanism to tell humans and computers apart.With the continuous development of pattern recognition and artificial intelligence technology,the traditional 2D static CAPTCHA reveals more and more security vulnerabilities,making it possible that some malicious network programs can initiate the program attack by cracking the CAPTCHA.This paper presents a safe and practical 3-layer dynamic CAPTCHA,creatively combining the single-frame zero-knowledge theory and the biological vision theory,thus making it not only difficult to identify a single frame,but also easy to recognize for humans.This design takes advantage of the weakness of computers in identifying multiple moving objects in a complex context,ensuring it still extremely hard for the computer programs to crack even using multiple frames.Hierarchical structure makes the CAPTCHA design much more clearly,bearing strong scalability and large space for optimization.
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paper_title: Multi-Modal CAPTCHA: A User Verification Scheme

paper_content:

CAPTCHA is an automated test that humans can pass, but current computer programs can't pass any program that has high success over a CAPTCHA can be used to solve an unsolved Artificial Intelligence (AI) problem. The most widely used CAPTCHAs rely on the sophisticated distortion of text images rendering them unrecognizable to the state of the art of pattern recognition techniques, and these text-based schemes have found widespread applications in commercial websites like free email service providers, social networking sites and online auction sites. The increase in bots breaking CAPTCHAs shows the ineffectiveness of the text-based CAPTCHAs that are used on most websites and Webmail services today. Bots can easily read the distorted letters and words using optical character recognition (OCR) or break the CAPTCHA using a dictionary attack. The weakness of each CAPTCHA scheme is summarized; accordingly we make an approach to build our CAPTCHA method. Considering the case study results and including other points which may pose difficulty for the OCR systems,we proposed a new technique to build a CAPTCHA which is multi-modal (Picture and Text based). An image is being rendered on the screen and many text labels drawn over it. A user has to identify the correct name of the underlying image among the set of text labels that are scattered over it, in order to pass a human verification test. We also proposed to use cursive text instead of plain text labels.
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paper_title: Protection through multimedia CAPTCHAs

paper_content:

CAPTCHAS which are well known as complete automatic public Turing test to tell computers and humans apart are a modern implementation of the Turing test, which ask a series of questions of two players: a human and computer. But both of the players pretend to be human. On the bases of the answers the judge has to decide which one is human and which one is computer, but the judge itself is a computer. In this article, we review current CAPTCHAs. After analysis of all the current CAPTCHAS we propose a new 3-D AI CATCHA which has all the strengths of existing CAPTCHAS to provide a better security alternative for ecommerce.
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paper_title: Protection through multimedia CAPTCHAs

paper_content:

CAPTCHAS which are well known as complete automatic public Turing test to tell computers and humans apart are a modern implementation of the Turing test, which ask a series of questions of two players: a human and computer. But both of the players pretend to be human. On the bases of the answers the judge has to decide which one is human and which one is computer, but the judge itself is a computer. In this article, we review current CAPTCHAs. After analysis of all the current CAPTCHAS we propose a new 3-D AI CATCHA which has all the strengths of existing CAPTCHAS to provide a better security alternative for ecommerce.
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paper_title: Protection through multimedia CAPTCHAs

paper_content:

CAPTCHAS which are well known as complete automatic public Turing test to tell computers and humans apart are a modern implementation of the Turing test, which ask a series of questions of two players: a human and computer. But both of the players pretend to be human. On the bases of the answers the judge has to decide which one is human and which one is computer, but the judge itself is a computer. In this article, we review current CAPTCHAs. After analysis of all the current CAPTCHAS we propose a new 3-D AI CATCHA which has all the strengths of existing CAPTCHAS to provide a better security alternative for ecommerce.
---
paper_title: Protection through multimedia CAPTCHAs

paper_content:

CAPTCHAS which are well known as complete automatic public Turing test to tell computers and humans apart are a modern implementation of the Turing test, which ask a series of questions of two players: a human and computer. But both of the players pretend to be human. On the bases of the answers the judge has to decide which one is human and which one is computer, but the judge itself is a computer. In this article, we review current CAPTCHAs. After analysis of all the current CAPTCHAS we propose a new 3-D AI CATCHA which has all the strengths of existing CAPTCHAS to provide a better security alternative for ecommerce.
---
paper_title: Protection through multimedia CAPTCHAs

paper_content:

CAPTCHAS which are well known as complete automatic public Turing test to tell computers and humans apart are a modern implementation of the Turing test, which ask a series of questions of two players: a human and computer. But both of the players pretend to be human. On the bases of the answers the judge has to decide which one is human and which one is computer, but the judge itself is a computer. In this article, we review current CAPTCHAs. After analysis of all the current CAPTCHAS we propose a new 3-D AI CATCHA which has all the strengths of existing CAPTCHAS to provide a better security alternative for ecommerce.
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paper_title: Making CAPTCHAs clickable

paper_content:

We show how to convert regular keyboard-entry CAPTCHAs into clickable CAPTCHAs. The goal of this conversion is to simplify and speed-up the entry of the CAPTCHA solution, to minimize user frustration and permit the use of CAPTCHAs on devices where they would otherwise be unsuitable. We propose a technique for producing secure clickable CAPTCHAs that are well suited for use on cell phones and other mobile devices. We support the practical viability of our approach by results from a user study, and an analysis of its security guarantees.
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paper_title: CAPTCHA Using Strangeness in Machine Translation

paper_content:

CAPTCHA is a technique that is used to prevent automatic programs from being able to acquire free e-mail or online service accounts. However, as many researchers have already reported, conventional CAPTCHA could be overcome by state-of-the-art malware since the capabilities of computers are approaching those of humans. Therefore, CAPTCHA should be based on even more advanced human-cognitive-processing abilities. We propose using the human ability of recognizing “strangeness” to achieve a new CAPTCHA. This paper focuses on strangeness in machine-translated sentences as an example, and proposes CAPTCHA using Strangeness in Sentences (SS-CAPTCHA), which detects malware by checking if users can distinguish natural sentences created by humans from machine-translated sentences. We discuss possible threats to SS-CAPTCHA and countermeasures against these threats. We also carried out basic experiments to confirm its usability by human users.
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paper_title: 3D CAPTCHA: A Next Generation of the CAPTCHA

paper_content:

Nowadays, the Internet is now becoming a part of our everyday lives. Many services, including Email, search engine, and web board on Internet, are provided with free of charge and unintentionally turns them into vulnerability services. Many software robots or, in short term, bots are developed with purpose to use such services illegally and automatically. Thus, web sites employ human authentication mechanism called Completely Automated Public Turing test to tell Computers and Humans Apart (CAPTCHA) to counter this attack. Unfortunately, many CAPTCHA have been already broken by bots and some CAPTCHA are difficult to read by human. In this paper, a new CAPTCHA method called 3D CAPTCHA is proposed to provide an enhanced protection from bots. This method based on assumption that human can recognize 3D character image better than Optical Character Recognition (OCR) software bots.
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paper_title: Protection through multimedia CAPTCHAs

paper_content:

CAPTCHAS which are well known as complete automatic public Turing test to tell computers and humans apart are a modern implementation of the Turing test, which ask a series of questions of two players: a human and computer. But both of the players pretend to be human. On the bases of the answers the judge has to decide which one is human and which one is computer, but the judge itself is a computer. In this article, we review current CAPTCHAs. After analysis of all the current CAPTCHAS we propose a new 3-D AI CATCHA which has all the strengths of existing CAPTCHAS to provide a better security alternative for ecommerce.
---
paper_title: Protection through multimedia CAPTCHAs

paper_content:

CAPTCHAS which are well known as complete automatic public Turing test to tell computers and humans apart are a modern implementation of the Turing test, which ask a series of questions of two players: a human and computer. But both of the players pretend to be human. On the bases of the answers the judge has to decide which one is human and which one is computer, but the judge itself is a computer. In this article, we review current CAPTCHAs. After analysis of all the current CAPTCHAS we propose a new 3-D AI CATCHA which has all the strengths of existing CAPTCHAS to provide a better security alternative for ecommerce.
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paper_title: Question-Based CAPTCHA

paper_content:

Today there are many Internet sites which require only the entry by human users but unfortunately some computer softwares called bots are designed by some hackers to enter these sites and use their resources through false registration. As a result some systems named CAPTCHA have been introduced to tell apart human users and computer software. This paper introduces a new CAPTCHA method. In this method a simple mathematical problem is generated according to a predefined pattern but instead of some object's name, we put their images. Then the whole problem is saved and shown to the user inform of an image to be answered by him. But since answering this problem requires four abilities of understanding text of question, detection of question images, understanding the problem, and solving the problem, only a human user can answer this question and present computer programs are unable to solve it. This project has been implemented by PHP language.
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paper_title: Multiple SEIMCHA: Multiple semantic image CAPTCHA

paper_content:

This paper presents a new semantic image CAPTCHA, called Multiple SEIMCHA. Multiple SEIMCHA system warps images by using geometric transformations and a 2d view of warped image is shown to user. Users should click on the upright orientation of warped image as a semantic. Multiple SEIMCHA evaluates user based on the idea of almost right response instead of completely right response. This idea uses hardness rate concept which is defined based on user response rate to images. The proposed system has a great response time and success rate as usability metrics and it is secure to bots.
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paper_title: CAPTCHA for children

paper_content:

In some websites it is necessary to distinguishing between human users and computer programs which is known as CAPTCHA (Completely Automated Public Turing test to tell Computers and Human Apart). CAPTCHA methods are mainly based on the weak points of OCR systems and using them are undesirable to human users. In this paper a method has been presented for distinguishing between human users and computer programs on the basis of choice of an object shown on the screen. In this method some objects are chosen randomly and the pictures of these topics are downloaded from the Internet. Then after applying some effects such as rotation, all of the pictures are shown on the screen. Then we ask the user to choose a specific object. Instead of writing the question, it is said using a TTS (Text-To-Speech) system. Therefore children who maybe illiterate and cannot read, can easily pass the test. If the user chooses the right object, we can guess that the user is a human being and not a computer program. This method is specially developed for children websites. The main advantage of this method is its simplicity because the user does not have to read or type anything.
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paper_title: Advanced Collage CAPTCHA

paper_content:

Some Internet Web sites for providing services to their customers, ask them to register in the Web site. Unfortunately hackers write programs to make automatic false enrollments which waste the Web site's resources. To solve this problem, systems known as CAPTCHA (completely automated public Turing test to tell computers and humans apart) have been introduced to distinguish between human user and computer program. One of the CAPTCHA methods is collage CAPTCHA. In this method some shapes are shown with distortion and the user is asked to choose a specific object. In this paper we increase the resistance of this method to attacks. For this purpose, we also show some other objects on the right of the screen. Some of these objects are same as the previous objects, but have the different shapes. Now we ask the user to choose a specific object and also its same object on the right of the screen. The user will be passed the test if he chooses the two similar objects correctly. In this method because the computer program should also recognize the similar object, the possibility of passing the test by computer is more reduced.
---
paper_title: Multi-Modal CAPTCHA: A User Verification Scheme

paper_content:

CAPTCHA is an automated test that humans can pass, but current computer programs can't pass any program that has high success over a CAPTCHA can be used to solve an unsolved Artificial Intelligence (AI) problem. The most widely used CAPTCHAs rely on the sophisticated distortion of text images rendering them unrecognizable to the state of the art of pattern recognition techniques, and these text-based schemes have found widespread applications in commercial websites like free email service providers, social networking sites and online auction sites. The increase in bots breaking CAPTCHAs shows the ineffectiveness of the text-based CAPTCHAs that are used on most websites and Webmail services today. Bots can easily read the distorted letters and words using optical character recognition (OCR) or break the CAPTCHA using a dictionary attack. The weakness of each CAPTCHA scheme is summarized; accordingly we make an approach to build our CAPTCHA method. Considering the case study results and including other points which may pose difficulty for the OCR systems,we proposed a new technique to build a CAPTCHA which is multi-modal (Picture and Text based). An image is being rendered on the screen and many text labels drawn over it. A user has to identify the correct name of the underlying image among the set of text labels that are scattered over it, in order to pass a human verification test. We also proposed to use cursive text instead of plain text labels.
---
paper_title: Protection through multimedia CAPTCHAs

paper_content:

CAPTCHAS which are well known as complete automatic public Turing test to tell computers and humans apart are a modern implementation of the Turing test, which ask a series of questions of two players: a human and computer. But both of the players pretend to be human. On the bases of the answers the judge has to decide which one is human and which one is computer, but the judge itself is a computer. In this article, we review current CAPTCHAs. After analysis of all the current CAPTCHAS we propose a new 3-D AI CATCHA which has all the strengths of existing CAPTCHAS to provide a better security alternative for ecommerce.
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paper_title: Motion CAPTCHA

paper_content:

In some Websites it is necessary to distinguish between human users and computer programs which is known as CAPTCHA (completely automated public turing test to tell computers and human apart). CAPTCHA methods are mainly based on the weaknesses of OCR systems while using them are undesirable to human users. In this paper a new CAPTCHA method is introduced on the basis of showing a movie of a personpsilas action. Then we ask the user to describe the movement of that person. The user should select the sentence which describes the motion from a list of sentences. If the user chooses the right sentence we can guess that the user is a human and not a computer program. The main advantage of this method is its simplicity and also the difficulty of computer attacks to it. This project has been implemented by PHP scripting language.
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paper_title: A Novel Image Based CAPTCHA Using Jigsaw Puzzle

paper_content:

Most commonly used CAPTCHAs are text-based CAPTCHAs which relay on the distortion of texts in the background image. With the development of automated computer vision techniques, which have been designed to remove noise and segment the distorted strings to make characters readable for OCR, traditional text-based CAPTHCAs are not considered safe anymore for authentication. A novel image based CAPTCHA which involves in solving a jigsaw puzzle is presented in this paper. An image is divided into an niAn (n=3, 4 or 5, depends on security level) pieces to construct the jigsaw puzzle CAPTCHA. Only two of the pieces are misplaced from their original positions. Users are required to find the two pieces and swap them. Considering the previous works which are devoted to solving jigsaw puzzles using edge matching technique, the edges of all pieces are processed with glitch treatment to prevent the computer automatic solving. Experiments and security analysis proved that human users can complete the CAPTCHA verification quickly and accurately, but computers rarely can. It is a promising substitution to the current text-based CAPTCHA.
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paper_title: Multiple SEIMCHA: Multiple semantic image CAPTCHA

paper_content:

This paper presents a new semantic image CAPTCHA, called Multiple SEIMCHA. Multiple SEIMCHA system warps images by using geometric transformations and a 2d view of warped image is shown to user. Users should click on the upright orientation of warped image as a semantic. Multiple SEIMCHA evaluates user based on the idea of almost right response instead of completely right response. This idea uses hardness rate concept which is defined based on user response rate to images. The proposed system has a great response time and success rate as usability metrics and it is secure to bots.
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Title: A SURVEY OF CURRENT RESEARCH ON CAPTCHA

Section 1: Definition of CAPTCHA
Description 1: This section defines CAPTCHA, explaining its purpose, functioning, and importance in distinguishing between humans and bots.

Section 2: Application of CAPTCHA
Description 2: This section describes various applications of CAPTCHA, including protecting website registration, shielding email addresses from scrapers, securing online polls, preventing dictionary attacks, and controlling search engine bots.

Section 3: History of CAPTCHAs
Description 3: This section provides a chronological overview of the development and milestones in the history of CAPTCHAs.

Section 4: Classification of CAPTCHAs
Description 4: This section categorizes CAPTCHAs into different types based on what is distorted, such as text, image, audio, video, and puzzle.

Section 5: CAPTCHA Based on Text
Description 5: This section explores various methodologies under text-based CAPTCHAs, including Gimpy CAPTCHA, EZ-Gimpy, PessimalPrint, Baffle Text, Scatter Type Method, Strangeness in Sentences CAPTCHA, and 3D CAPTCHA.

Section 6: CAPTCHA Based on Image
Description 6: This section discusses different image-based CAPTCHAs, such as Bongo, Pix CAPTCHA, Hand-Written CAPTCHA Method, Implicit CAPTCHA Method, Drawing CAPTCHA Method, CAPTCHA Systems for Nintendo, CAPTCHAs for Children, Collage CAPTCHA, Advanced Collage CAPTCHA, and Online Collage CAPTCHA.

Section 7: CAPTCHA Based on Audio
Description 7: This section covers audio-based CAPTCHAs, detailing methods like Text-To-Speech conversion and spoken CAPTCHAs for blind users.

Section 8: CAPTCHA Based on Video
Description 8: This section examines video-based CAPTCHAs, specifically the Motion CAPTCHAs method.

Section 9: CAPTCHA Based on Puzzle
Description 9: This section describes puzzle-based CAPTCHAs and the different methods used, such as Multiple SEIMCHA.

Section 10: Strength and Weakness of CAPTCHA Based on Image
Description 10: This section discusses the strengths and weaknesses of image-based CAPTCHAs, highlighting issues like user accessibility and bot susceptibility.

Section 11: Strength and Weakness of CAPTCHA Based on Audio
Description 11: This section evaluates the strengths and weaknesses of audio-based CAPTCHAs, considering aspects like accessibility for visually impaired users and potential user confusion.

Section 12: Strength and Weakness of CAPTCHA Based on Video
Description 12: This section reviews the strengths and weaknesses of video-based CAPTCHAs, addressing concerns such as download issues and language barriers.

Section 13: Strength and Weakness of CAPTCHA Based on Puzzle
Description 13: This section analyzes the strengths and weaknesses of puzzle-based CAPTCHAs, including user experience and accessibility challenges.

Section 14: Conclusions
Description 14: This section summarizes the significance of CAPTCHAs in web security, reviews the discussed classification methods, and suggests developing multi-linguistic CAPTCHAs.