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Revision as of 23:46, 29 March 2015
What is CAPTCHA:
Completely Automated Public Turing Test to Tell Computers and Humans Apart
As the name suggests, Captcha is a test designed to distinguish humans from bots by providing an identification mechanism that would be difficult for the latter to circumvent, but not for humans. The origins of CAPTCHA lay within the hacking community, they were originally used as a method for allowing users to post about sensitive topics without having to worry about being monitored by lurking authorities. An example of this is leetspeak (1337 or Leet), which would convert words into look-alike characters.
CAPTCHA took a form that is more similar to the one we know currently in 1997, when the AltaVista team began working on a system to prevent Internet bots from adding active URLs to the AltaVista search engine platform. At the time, this was achieved by building puzzles and images which would not be possible to read with the help of OCR. Ulterior versions would be made by Luis von Ahn, Manuel Blum, Nicholas J. Hopper and John Langford, who coined the term in 2003.
With reCAPTCHA, the useless puzzles were replaced with text that was unrecognized by OCR during book digitisations. The new model would contribute to making knowledge readily available in a digital format while proving to be effective against unwanted visitors. reCAPTCHA was bought in 2009 by Google and since 2012 has been used to determine the house numbers from the Street View project.