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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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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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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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