The term "CAPTCHA" was coined in 2000 by Luis von Ahn, Manuel Blum,Nicholas J. Hopper, and John Langford (all of Carnegie Mellon University). It is anacronym based on the word "capture" and standing for "Completely AutomatedPublic Turing test to tell Computers and Humans Apart". Carnegie Mellon University attempted to trademark the term,[1] but the trademark application was abandoned on 21 April 2008.
A CAPTCHA is sometimes described as a reverse Turing test, because it is administered by a machine and targeted at a human, in contrast to the standardTuring test that is typically administered by a human and targeted at a machine.
