CAPTCHA- The Furtive Behind Squiggly Computer Letters.

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                                                      A CAPTCHA an acronym for "Completely Automated Public Turing test to tell Computers and Humans Apart". It is a type of challenge response test used in computing to determine whether the user is human or not.
                                                            The term was coined in 2003 by Luis von Ahn, Manuel Blum, Nicholas J. Hopper, and John Langford. The most common type of CAPTCHA was first invented in 1997 by two groups working in parallel:  Mark D. Lillibridge, Martin Abadi, Krishna Bharat, and Andrei Z. Broder; and Eran Reshef, Gili Raanan and Eilon Solan. This form of CAPTCHA requires that the user type the letters of a distorted image, sometimes with the addition of an obscured sequence of letters or digits that appears on the screen. Because the test is administered by a computer, in contrast to the standard Turing test that is administered by a human, a CAPTCHA is sometimes described as a reverse Turing test.
                                                    So, let’s see exactly what is Turing Test. In 1950’s a scientist named Alan Turing conducted an experiment to distinguish between AI (computers) and humans. He wrote some algorithms on AI which are now used in implementing AI.
                                                  The captcha code is mainly used in online booking websites (any category). So, let’s see the history about it. Two people introduced this captcha code because when they want to book a ticket for basketball match they booked a ticket from online website and when they booked two tickets because of bots in the system instead of two tickets it has booked all the available tickets to them. So, they want to control that bot and came up with a CAPTCHA code which is not understandable by the robot (computer). Later this technology was taken by a popular search engine AltaVista and GOOGLE.
                                 This user identification procedure has received many criticisms, especially from disabled people, but also from other people who feel that their everyday work is slowed down by squiggle words that are difficult to read. It takes the average person approximately 10 seconds to solve a typical CAPTCHA. So, GOOGLE modified it and renamed as reCAPTCHA, which has received many criticisms and it was a failure.
                                        Again, GOOGLE has modified it and renamed as “NoCAPTCHA reCAPTCHA” which was very successful in which it contains images to verify a human or a robot. Now a days most of the websites are implementing this technology to secure from bots.





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