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  • Chellapilla, Kumar and Patrice Simard. "Using Machine Learning to Break Visual Human Interaction Proofs (HIPS)." Microsoft Research. (Aug. 6, 2008) http://research.microsoft.com/~kumarc/pubs/chellapilla_nips04.pdf
  • Chew, Monica and J.D. Tygar. "Collaborative Filtering CAPTCHAs." In Human Interactive Proofs: Second International Workshop. 2005. (Aug. 4, 2008) http://www.cs.berkeley.edu/~tygar/papers/Collaborative_filtering_CAPTCHAs.pdf
  • Jongsma, Carl. "Breaking Google's audio CAPTCHA." Computerworld. May 2, 2008. (Aug. 4, 2008) http://www.networkworld.com/news/2008/050208-breaking-googles-audio.html
  • Leyden, John. "Spammers crack Gmail CAPTCHA." The Register. Feb. 25, 2008. (Aug. 5, 2008) http://www.theregister.co.uk/2008/02/25/gmail_captcha_crack/
  • Mori, Greg and Jitendra Malik. "Breaking a Visual CAPTCHA." Simon Fraser University. (Aug. 4, 2008) http://www.cs.sfu.ca/~mori/research/gimpy/
  • Oppy, Graham and David Dowe. "The Turing Test." Stanford Encyclopedia of Philosophy. April 9, 2003. (Aug. 5, 2008) http://plato.stanford.edu/entries/turing-test/
  • Thompson, Clive. "For Certain Tasks, the Cortex Still Beats the CPU." Wired. June 25, 2007. (Aug. 5, 2008) http://www.wired.com/techbiz/it/magazine/15-07/ff_humancomp
  • Vaughan-Nichols, Steven J. "How CAPTCHA got trashed." Computerworld. July 15, 2008. (Aug. 5, 2008) http://www.computerworld.com.au/index.php/id;489635775;fp;;fpid;
  • Von Ahn, Luis. "Human Computation." Google TechTalks. July 26, 2006. (Aug. 6, 2008) http://video.google.com/videoplay?docid=-8246463980976635143
  • Von Ahn, Luis, Manuel Blum and John Langford. "Telling Humans and Computers Apart Automatically." Communications of the ACM. Feb. 2004. Vol. 47, No. 2. (Aug. 4, 2008) http://www.cs.cmu.edu/~biglou/captcha_cacm.pdf
  • Von Ahn, Luis, Manuel Blum and John Langford . "Using Hard AI Problems for Security." Computer Science Department -- Carnegie Mellon University. ( Aug. 4, 2008) http://www.captcha.net/captcha_crypt.pdf
  • W3C Working Group Note. "Inaccessibility of CAPTCHA." W3C. Nov. 23, 2005. (Aug. 4, 2008) http://www.w3.org/TR/turingtest/

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