10.2. RadCaptcha

Completely Automated Public Touring test to tell Computers and Humans Apart (CAPTCHA) was developed by a team of researchers in Carnegie Mellon University composed of Luis von Ahn, Manuel Blum, Nicholas Hopper, and John Langford, who were asked by Yahoo for a way to stop automated bots that were creating thousands of accounts for malicious uses.

The solution was to present a set of characters that are impossible for a computer program to read but are somewhat easy for humans. In compliance with accessibility standards, an audio file describing the set of characters is also provided. If the set of characters is correctly confirmed by the user, the system allows that user to enter the site or perform whatever task the CAPTCHA ...

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