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 (kăp′chə) Computers
A security feature, as on a webpage, that attempts to distinguish between legitimate human users and bots by requiring users to perform a mildly challenging task such as deciphering distorted text.

[Acronym of c(ompletely) a(utomated) p(ublic) T(uring test to tell) c(omputers and) h(umans) a(part), coined in 2000 by the researchers who developed the security feature and intended to suggest a colloquial pronunciation of capture.]
American Heritage® Dictionary of the English Language, Fifth Edition. Copyright © 2016 by Houghton Mifflin Harcourt Publishing Company. Published by Houghton Mifflin Harcourt Publishing Company. All rights reserved.


(Communications & Information) a test in which the user of a website is asked to decipher a distorted image, used to protect the website against automated attacks
[C21: acronym for C(ompletely) A(utomated) P(ublic Turing Test to) T(ell) C(omputers and) H(umans) A(part)]
Collins English Dictionary – Complete and Unabridged, 12th Edition 2014 © HarperCollins Publishers 1991, 1994, 1998, 2000, 2003, 2006, 2007, 2009, 2011, 2014
References in periodicals archive ?
[11] Zhu, B., Captcha as Graphical Passwords-A New Security Primitive Based on Hard AI Problems, IEEE Transactions on Information Forensics and Security, Vol.9, No.6, 2014, pp.
For the original CAPTCHA images consisting of warped and obscured text, the generation script was designed to create any number of testable images, and the level of obscuration was carefully matched to what was relatively easy for most humans while being nearly impossible for machines.
Solve Media's Type-In technology creates extremely effective branding opportunities to engage consumers through Captcha, display, video, pre-roll and mobile formats.
Silver: The Human Captcha, Microsoft/ Starcom Mediavest (see Digital: Mobile winner on page 22).
These security considerations include restricted requests number from a particular IP address and presence of Captcha codes in such pages [9],
As an extension of the second type, the aim of this study is to propose a practical CAPTCHA scheme for image annotation that can be applied even if a target attribute (for annotation) is not clearly separated into mutually exclusive categories.
"Captcha" stands for "completely automated public Turing test to tell computers and humans apart." The tests were created in 2000 by researchers at Carnegie Mellon University and are solved by millions of Web users daily.
He wanted a program that could "go through the buying process (including writing out the captcha) until the payment page".
They can be used to send email spam, launch distributed denial-of-service attacks, solve CAPTCHA challenges on websites, perform online banking fraud or click fraud and many other activities.
Other chapters explore graphical passwords, SQL injection attack countermeasures, scrambled CAPTCHA, collaborative enterprise security, electronic voting systems, and mobile codes for wireless sensor networks.