Gadgetopia

Captcha: Those little “distorted text in a picture” thingies have a name. Who knew?

A captcha (an acronym for “completely automated public Turing test to tell computers and humans apart”) is a type of challenge-response test used in computing to determine whether or not the user is human. […]

A common type of captcha requires that the user type the letters of a distorted and/or obscured sequence of letters or digits that appears on the screen. Because the test is administered by a computer, in contrast to the standard Turing test that is administered by a human, a captcha is sometimes described as a reverse Turing test.