A CAPTCHA is a type of challenge-response test used in computing to ensure that the response is not generated by a computer. For example, humans can read distorted text, but current computer programs can't.
The term CAPTCHA (for Completely Automated Turing Test To Tell Computers and Humans Apart) was coined in 2000 by Luis von Ahn, Manuel Blum, Nicholas Hopper and John Langford of Carnegie Mellon University. At the time, they developed the first CAPTCHA to be used by Yahoo.
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