Captcha is a type of challenge-response test used in computing to ensure that the response is not generated by a computer. The process usually involves one computer (a server) asking a user to complete a simple test which the computer is able to generate and grade. Because other computers are unable to solve the CAPTCHA, any user entering a correct solution is presumed to be human. Thus, it is sometimes described as a reverse Turing test, because it is administered by a machine and targeted to a human, in contrast to the standard Turing test that is typically administered by a human and targeted to a machine. A common type of CAPTCHA requires that the user type letters or digits from a distorted image that appears on the screen.
Moni Naor was the first person to theorize a list of ways to verify that a request comes from a human and not a bot. Primitive CAPTCHAs seem to have been developed in 1997 by Andrei Broder, Martin Abadi, Krishna Bharat, and Mark Lillibridge to prevent bots from adding URLs to their search engine. In order to make the images resistant to OCR (Optical Character Recognition), the team simulated situations that scanner manuals claimed resulted in bad OCR. In 2000, Luis von Ahn and Manuel Blum coined the term 'CAPTCHA', improved and publicized the notion, which included any program that can distinguish humans from computers. They invented multiple examples of CAPTCHAs, including the first CAPTCHAs to be widely used, which were those adopted by Yahoo!.
I'll set the scene up for you: You're eager to start posting on an awesome new website that sounds really interesting (...say, Lunch.com! *) You get through all the registration steps- name, email, password, password verification, yada yada...and then you see this weird blurry smudge at the bottom of the page. It looks like this: Orr, if you're really having a bad day, it could look as convoluted as this: … more
90% of the time I have no problem reading it. However, once I got what looked like the starting set-up of the board game Othello. . . if you don't know what that is, it's four circles arranged in a square--one kitty-corner set black, the other white. . . I took a pic with my phone, if I ever figure out how to get that here I'll show you. But do tell, how do I type that?!?