A CAPTCHA or Captcha (pronounced /ˈkæptʃə/) is a type of challenge-response ccp test 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 clep 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.The term "CAPTCHA" (based upon the word capture) was coined in 2000 by Luis von Ahn, Manuel Blum, Nicholas mcat exam . Hopper, and John Langford (all of Carnegie Mellon University). It is a contrived acronym for "Completely Automated Public Turing test to tell Computers and Humans Apart." Carnegie Mellon cdl test University attempted to trademark the term,[2] but the trademark application was abandoned on 21 April 2008.[3]

I visited this sight for the first time and found it much informative and knowledgeable but I would like to add that currently we are living in the era of IT but unfortunately more than half of world population is illiterate. Out of those a few are computer and internet familiar so the target market for internet marketing is niche. Therefore the developed nations should promote IT as well as computer literacy in these developing areas so the target market can be increased in future.

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