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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.]


(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)]
References in periodicals archive ?
In answering PayPal and Yahoo Captchas, the system achieved an accuracy rate of greater than 50 per cent.
Other Captchas that it can beat are BotDetect, with a 64.
7] introduced the idea of showing several textual CAPTCHAs into a grid of clickable CAPTCHAs.
Fourthly, the Labour attack which some information specifies that there are free or low-cost third-party human labour to crack CAPTCHAs.
The main use of CAPTCHAs is to prevent bots from using various computing services or collecting sensitive information like poll results, nominations and registering free email accounts or collect email addresses, and help prevent spam [5].
While excited about their progress, Heshmat also states concern about the method being used to defeat captchas on websites.
CleanTalk detects and stops spam witout CAPTCHAs or other math-based, human/bot testing techniques.
What s worse, the user experience today is a really bumpy ride registrations, logins, CAPTCHAs, and verification emails present significant obstacles for both the users and the service providers, and contribute to very low conversion rates.
CAPTCHAs have been used by many websites to tell whether their user is a human or a computer, and, in this way, they prevent abuse from malicious bots (automated programs) that are usually written to generate spam.
CAPTCHAs ask users to read and retype a small string of random, visually distorted text.
An artificial-intelligence company called Vicarious says its technology can solve numerous types of Captchas more than 90 percent of the time.
Captchas usually come in the form of graphic depictions of warped text, requiring users to type the distorted words they see on the screen (Figure 1).