CAPTCHA stands for Completely Automated Public Turing Test to tell Computers and Humans Apart. It was coined coined in 2000 by Luis von Ahn, Manuel Blum, Nicholas J. Hopper of Carnegie Mellon University and John Langford of IBM.
Typically, CAPTCHAs require website viewers to type a short series of letter displayed in distorted fashion. The theory is that computers would not be able to interpret the distorted letters, but humans would. CAPTCHAs sometimes take the form of a short math (1 + 3 = ?) or logic problem (Dog, Cat, Fish, Apple: which one doesn't belong?).
CAPTCHAs are intented to prevent automated processes (spiders, spambots, etc.) from accessing data or filling out forms.
CAPTCHAs have also been used to crowdsource the conversion of scanned documents to machine-readable form.
Return to the main menu.