CAPTCHA (redirected from Visual confirmation)

(Completely Automated Public Turing test to tell Computers and Humans Apart) A category of technologies used to ensure that a human is making the transaction online rather than a computer. Developed at Carnegie Mellon University, random words or letters are displayed in a distorted fashion so that they can be deciphered by people, but not by software. Users are asked to type in what they see on screen to verify they are, in fact, human.

CAPTCHAs Baffle Bots
Bots (software agents) have been developed to automatically perform illegitimate transactions over the Web, including overloading online opinion polls, performing dictionary attacks to find names and passwords as well as grabbing thousands of free e-mail accounts for sending spam. CAPTCHAS can be used to prevent such transactions as they ensure that a real person made the transaction.

CAPTCHAs Get Tougher
After CAPTCHAS were deployed in 2001, bots were created to circumvent them by analyzing the distorted images, requiring even more sophisticated CAPTCHA techniques. Instead of using real words from a list, made-up words are used with more distortion in the background. Non-text approaches have also been added; for example, showing a series of images and asking the user to type in what is common in all of them, perhaps an apple or some other object. See reCAPTCHA, dictionary attack and Turing test.

The CAPTCHA Concept

Random words or letters are displayed as in the above examples, and users are asked to type in what they see. The text is camouflaged so that only humans can decipher it. (Images courtesy of Carnegie Mellon School of Computer Science, www.captcha.net)