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10/08/2004: "Human Interface Proof for ASP.NET"

In 2000, Yahoo was searching for an answer to this very problem. Their chief scientist, Udi Manber, recruited the help of Carnegie Mellon professor Manual Blum, and with the aid of one of Blum's Ph.D. students, Luis von Ahn, they created CAPTCHA. CAPTCHAs, or more specifically "Completely Automated Public Turing Tests to Tell Computers and Humans Apart," are based on the RTT scenario and are a kind of Human Interactive Proof (HIP), presenting to a user a puzzle that should be easily solvable by a human but difficult for a computer. In essence, they take advantage of the intelligence gap that exists between humans and computers. CAPTCHAs differ from the standard Turing Test in that they're "completely automated," meaning that the questions or puzzles posed to the user come from a computer, and thus must be able to be generated automatically. CAPTCHA-based systems are now in use all over the Web, from large Internet portals like Yahoo and MSN to smaller, individually run personal sites.
Read more about HIP and download the library.