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A typical representation of a CAPTCHA


Coined by a team of researchers at Carnegie Mellon University in 2000 as a loose Acronym of "Completely Automated Public Turing test to tell Computers and Humans Apart".



  1. A CAPTCHA is a human response test that requires you to enter a series of letters and/or numbers and/or symbols correctly to prove you are a human and not a computer program attempting to spam the site.
  2. (by extension) Anything that a human must do to prove that they are not a computer.

Derived terms[edit]

  • audio CAPTCHA, a distorted audio file containing a voice reading numbers.
  • visual CAPTCHA, when a distinction must be made between an audio CAPTCHA and a distorted image.


Usage notes[edit]

Although occasionally spelt with lowercase letters (captcha), or with an initial uppercase letter (Captcha), most authors remain aware of its origin as an acronym and use uppercase.

Carnegie Mellon University abandoned their attempt to trademark this term in 2008, as usage was already too widespread. (USPTO file number 78500434).

See also[edit]