Understanding CAPTCHA: Definition, Types, and Applications

www.studymafia.org Seminar On CAPTCHA Submitted To: www.studymafia.org www.studymafia.org Submitted By:

CONTENT Introduction Definition Bascilly what a Captcha do ? How does Captcha work? Types of Captchas Breaking Captchas Characteristics Applications Conclusion

INTRODUCTION Computers and Humans are apart , a technique used by a computer to tell if it is interacting with human or some other computer. It is needed because activities such as online commerce transactions, search engine submissions, Web polls, Web registrations, free e-mail service registration and other automated services are subject to software programs, or bots, that mimic the behavior of humans in order to skew the results of the automated task or perform malicious activities, such as gathering e-mail addresses for spamming.

DEFINITION A CAPTCHA (an acronym for "completely automated public turing test to tell computers and humans apart") is a type of challenge-response test used in computing to determine whether or not the user is human. A CAPTCHA is a program that can generate and grade tests that: Most humans can pass, but Current computer programs can't pass

BASCILLY WHAT A CAPTCHA DO ? In order to validate the digital transaction, using the CAPTCHA system the user is presented with a distorted word typically placed on top of a distorted background. The user must type the word into a field in order to complete the process. Computers have a difficult time decoding the distorted words while humans can easily decipher the text. Some CAPTCHAs now use pictures instead of words where the user is presented with a series of pictures and asked what the common element among all of the pictures is. By entering that common element, the user validates the transaction and the computer knows it is dealing with a human and not a bot.

HOW DOES A CAPTCHA WORKS? A CAPTCHA image shows a random string which the user has to type to submit a form. This is a simple problem for humans, but a very hard problem for computers which have to use character recognition, especially, because the displayed string is alienated in a way, which makes it very hard for a computer to decode.

TYPES OF CAPTCHA Text based Gimpy, ez-gimpy Gimpy-r, Google CAPTCHA Simard s HIP (MSN) Graphic based Bongo Pix Audio based

Text based CAPTCHAs Gimpy, ez-gimpy Pick a word or words from a small dictionary Distort them and add noise and background Gimpy-r, Google s CAPTCHA Pick random letters Distort them, add noise and background Simard s HIP Pick random letters and numbers Distort them and add arcs

Graphic based CAPTCHAs Bongo Display two series of blocks User must find the characteristic that sets the two series apart User is asked to determine which series each of four single blocks belongs to Difference? thick vs. thin lines

Graphic based CAPTCHAs PIX Create a large database of labeled images Pick a concrete object Pick four images of the object from the images database Distort the images Ask the user to pick the object for a list of words

Audio based CAPTCHAs Pick a word or a sequence of numbers at random Render them into an audio clip using a TTS software Distort the audio clip Ask the user to identify and type the word or numbers

BREAKING CAPTCHAS Most text based CAPTCHAs have been broken by software OCR Segmentation Other CAPTCHAs were broken by streaming the tests for unsuspecting users to solve.

CHARACTERISTICS They are completely automated. This avoids the necessity for human maintenance or intervention in the test, with obvious benefits in cost and reliability. The algorithm used is made public, though it may be encumbered by a patent. This is stipulated so as to require that breaking a captcha requires the solution of a hard problem in the field of artificial intelligence (AI) rather than just the discovery of the (secret) algorithm, which could be obtained through other techniques.

APPLICATIONS Online polls Search engine bots Worms and spams Search Engine Bots Prevent dictionary attacks

CONCLUSION CAPTCHAS are any software that distinguishes human and machine. Research in CAPTCHAS implies advancement in AI making computers understand how human thinks. Internet companies are making billions of dollars every year, their security and services quality matters and so does the advancement in CAPTCHA technology.

REFERENCE www.google.com www.wikipedia.com www.studymafia.org

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