Applications of CAPTCHA

Applications of CAPTCHARamteen TalibCAPTCHA is a powerful toolQingkun Ramteen TalibA CAPTCHA or Captcha is a type of challenge-response test utilise in to computation o ensure that the response is not generated by a computer.CAPTCHA requires that the user type letters or digits from a belieed pictorial matter that appears on the screen. whatever user entering a correct solution is presumed to be human else user is bot and denied access.It is sometimes described as a reverse Turing test.OCRs(Optical Character Recognition) be not able to ascertain CAPTCHAsCharacteristeicsA CAPTCHA is a means of automatically generating new challenges whichCurrent software is unable to solve accurately.Most humans stop solveDoes not rely on the type of CAPTCHA being new to the attacker.CAPTCHAs rely on difficult problems in artificial intelligenceOrigin world-class developed by Alta Vistain 1997.The term coined in 2000 by Luis von Ahn, Manuel Blum and Nicholas J. Hopper of Carnegie Mellon Univers ity and John Langford of IBM.Primitive CAPTCHAs seem to have been developed in 1997 by Andrei Broder, Martin Abadi, Krishna Bharat, and Mark Lillibridge to hold on bots from adding URLs to their search engine.Turning TestProposed by Alan TuringTo test a machines level of intelligence Human judge asks questions to two participants, one is a machine, he doesnt last which is which, If judge cant tell which is the machine, the machine passes the test.CAPTCHA employs a reverse Turing test,Judge = CAPTCHA program ,Participant = userif user passes CAPTCHA, he is humanIf user fails, it is a machineTypes of CAPTCHAs1.Text Based CAPTCHAs2.Graphics Based CAPTCHAs3.Audio or Sound Based CAPTCHAsText BasedTypically relay on sophisticated distortion of text images make them unrecognizable to the state of the art of the pattern intuition programs but recognizable by humans.ExamplesSimple, normal language questionsWhat is sum of three and thirty-five?If to solar day is Saturday, what is day afte r tomorrow?Very effective, needs a large question bankCognitively challenged users find it hard .GimpyOriginally designed by hayseed and CMU.Based on human ability to read heavily distorted and corrupted text.works by choosing a certain number of words from a dictionary, and then displaying them corrupted and distorted in an image after that Gimpy asks the user to type the words displayed in that image.EZ-GimpyA modified version of Gimpy.Used in Yahoo Messenger Service.It contains only one random character string.The word is random and not picked from the dictionary.Its not a good implementation of CAPTCHA, and already overturned OCRs.MSN Passport service CAPTCHAsits provided for Microsoft MSN services.uses 8 characters.Warping is used to distort.Its very strongly implemented and hasnt been brokenGraphic Based CAPTCHAsRequires user to perform image recognition test.ExamplesIMAGINATIONCAPTCHA that requires two steps to be passed.first step visitor clicks elsewhere on the picture th at composed of a few images and selects in this way a single image.second step the selected image is loaded. It is enlarged but very distorted. Also variants of the answer are loaded on the leaf node side. The visitor should select a correct answer from the set of the proposed words.BONGOAfter M.M.Bongard, pattern recognition expert.User has to solve a pattern recognition problem.ASSIRAAnimal Species Image Recognition for Restricting Access.Its a HIP that works by asking users to identify photographs of cats and dogs.Difficult for computers but humans can execute it very quickly and accurately.Audio CAPTCHAsRequire user to solve a speech recognition test.In this version of captcha letters are read clamorously instead of being displayed in an image.Helps visually disabled usersBelow is the Googles audio enabled CAPTCHA.3D CAPTCHA3DCaptcha is the captcha nice to humans, bad to machines.It is written in PHP.A new barbel to captchas, using humans spatial cognition abilities to diffe rentiate humans from machines.It uses a markov-chain to generate words that resemble human language and are easy to type, except avoid dictionary lookups.It filters profane language.Its easy to deploy.Re-CAPTCHAFree CAPTCHA service that helps to digitize books, newspapers and old time radio shows.reCAPTCHA improves the process of digitizing books by sending words that cannot be read by computers to theWeb in the form of CAPTCHAs for humans to decipher.Each word that cannot be read correctly by OCR is placed on animage and used as a CAPTCHA.This is possible because most OCR programs alert you when a wordcannot be read correctly.Working of reCAPTCHATwo words are shown, one word is know as Control Word, and another one is known a questionable word.System assumes that if human types the control word correctly, the questionable word is also correct.The identification performed by each OCR program is given a value of 0.5 points, and each interpretation by a human is given a full point. once a given identification hits 2.5 votes, the word is considered called.ApplicationsPreventing Comment Spam in BlogsProtecting Website RegistrationProtecting Email Address From ScrapersOnline PollsPreventing Dictionary Attacks search Engine BotsWorms and SpamAdvancing Artificial IntelligenceCalled Hard-AI problems.CAPTCHA tests are based on open problems in artificial intelligence (AI).A win-win scenarioEither a CAPTCHA is not broken and there is a way to differentiate humans from computers.Or the CAPTCHA is broken and an AI problem is solved. Thus AI knowledge is march on if CAPTCHAs are broken.V/SConstructing CAPTCHAsThings to keep in mindDont store CAPTCHA solution in Web pages meta dataA CAPTCHA is no good if it doesnt distortNeed a large database of different CAPTCHA questionsAvoid repetition of questionsCAPTCHA LogicGenerate the questionPersist the correct answerPresent the question to userEvaluate answer, if incorrect, start again-Generate a different CAPTCHAIf correct, al low access to userGuidelinesAccessibilityImage securityScript securitySecurity after general adoptionCustom implementation or a general CAPTCHA?Breaking CAPTCHAsCracking CAPTCHAs through programsConvert CAPTCHA into greyscaleDetect patterns in the image corresponding to charactersOr, read session files of that user and know the CAPTCHA wordSolution Only store a hash of the CAPTCHA word in session filesIssues with CAPTCHAsUsability issuesW3C mandatesWeb to be getatable to all peopleSome CAPTCHAs are inaccessible to visually impaired, cognitively challenged peopleCompatibility issuesJavaScript may need to be activated in browsersSome may need Adobe Flash plugin installedReal WorldConclusionCAPTCHAs are an effective way to counter bots and reduce spamThey serve dual adjudicatehelp advance AI knowledgeApplications are variedfrom stopping bots to character recognition pattern matchingSome issues with current implementations represent challenges for future improvements