Definition of captcha
: a test to prevent spamming software from accessing a website by requiring visitors to the site to solve a simple puzzle (typically by reading and transcribing a series of numbers or letters from a distorted image) in order to gain access The point of the CAPTCHA is that reading those swirly letters is something that computers aren't very good at. If you can read them, you're probably not a piece of software run by a spammer. — Leviticus Grossman
Origin and Etymology of captcha
Completely Automatic Public Turing test to tell Computers and Humans Apart (with deliberate pun on 1capture)
First Known Use: 2001
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