Something That Human Can Do But Computers Can’t………..

CAPTCHA

Presented By : Shreya

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DefinitionCAPTCHA stands for Completely

Automated Public Turing test to tell Computers and Humans Apart

A program that can tell whether its user is a human or a computer.

The challenge: develop a software program that can create and grade challenges most humans can pass but computers cannot

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Background First used by Altavista in1997

Reduced SPAM add-url by over 95% CMU/Yahoo!

Automated the creating and grading of challenges

PARCRelies on document image degradation to

prevent successful OCRConducted user-focused studies to assess the

effectiveness of CAPTCHAs

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BackgroundCAPTCHAs are based on open AI

problemsBreaking CAPTCHAs help advance

AI by solving these open problemsImproving CAPTCHAs help telling

computers and human apartWin-win situation

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ApplicationsFree email servicesOnline pollsDictionary attacksNewsgroups, Blogs, etc…SPAM

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Types of CAPTCHAsText based

Gimpy, ez-gimpyGimpy-r, Google CAPTCHASimard’s HIP (MSN)

Graphic basedBongoPix

Audio based

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Text Based CAPTCHAsGimpy, ez-gimpy

Pick a word or words from a small dictionaryDistort them and add noise and background

Gimpy-r, Google’s CAPTCHAPick random lettersDistort them, add noise and background

Simard’s HIPPick random letters and numbersDistort them and add arcs

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Text Based CAPTCHAs

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Graphic Based CAPTCHAsBongo

Display two series of blocksUser must find the characteristic that sets the

two series apartUser is asked to determine which series each

of four single blocks belongs to

Difference? thick vs. thin lines

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Graphic Based CAPTCHAsPIX

Create a large database of labeled imagesPick a concrete objectPick four images of the object from the images

databaseDistort the imagesAsk the user to pick the object for a list of

words

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Graphic Based CAPTCHAs

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DogPool

Audio Based CAPTCHAsPick a word or a sequence of numbers at

randomRender them into an audio clip using a TTS

softwareDistort the audio clipAsk the user to identify and type the word or

numbers

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Breaking CAPTCHAsMost text based CAPTCHAs have been

broken by softwareOCRSegmentation

Other CAPTCHAs were broken by streaming the tests for unsuspecting users to solve.

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Properties CAPTCHA should be automatically generated

and graded Test can be taken quickly and easily by human

users Test will accept virtually all human users and

reject software agents Test will resist automatic attack for many years

despite the technology advances and prior knowledge of algorithms

Final ThoughtsThey are crucial to preventing boot attacksHopefully, they will become more user-

friendly to people with disabilities (visual, mental)

CAPTCHA’s are mainly produced from AJAX and PHP technology

Various algorithms are presentUse of XML

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Bibliography……Bibliography……

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