What is CAPTCHA?


CAPTCHA is an automated system which tests a visitor to a website to verify that they are human.

A CAPTCHA requires the person submitting information to complete a test, usually a visual one, that only a human could complete.
This could involve showing a picture of text, distorted enough that a human can recognise it but a machine couldn’t if scanning it automatically.

New alternatives to CAPTCHA simply ask humans to click a box, asking “are you a human?”

CAPTCHAs are used when there is a threat that an automated piece of software called a bot might submit information for spam purposes or to extract data from websites.

When is a  CAPTCHA required?

Technology Term:

Completely Automated Public Turing test

Standard Definition Exists?

A computer program or system intended to distinguish human from machine input, typically as a way of thwarting spam and automated extraction of data from websites.

Accepted Acronym:


Year first used/coined:


Attributed to:

Luis von Ahn, Manuel Blum, Nicholas J. Hopper, and John Langford

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