definition of CAPTCHA
an acronym which describes a program that protects websites from spammers by providing a test (e.g. a distorted text) which humans can do but computers cannot. It stands for 'Completely Automated Public Turing Test To Tell Computers and Humans Apart' and is a trademark of Carnegie Mellon University. There are visual as well as audio captchas in use.
Recognising the kinds of characters used in CAPTCHAs remains a significant challenge in computer vision.
Submitted on 28/09/2009 09:37:00