Abstract :
Use of INTERNET has remarkably
increased Globally in the past 10-12 years and so is the need of the Security over it. Marketing and
Advertisement over INTERNET has seen companies like GOOGLE being made, which at the moment is traded at 181 billion USD ie. Almost twice of General
Motors, McDonalds combined.
You're trying to sign up for a free
email service offered by Gmail or Yahoo. Before you can submit your
application, you first have to pass a test. It's not a hard test -- in fact, that's
the point. For you, the test should be simple and straightforward. But for a
computer, the test should be almost impossible to solve. This sort of test is a
CAPTCHA. They're also known as a type of Human Interaction Proof(HIP). You've probably seen CAPTCHA tests on lots of Web sites. The most
common form of CAPTCHA is an image of several distorted letters. It's your job
to type the correct series of letters into a form. If your letters match the ones in the
distorted image, you pass the test.
CAPTCHAs are short for Completely Automated Public Turing test to tell Computers and Humans Apart. The term
"CAPTCHA" was coined in 2000 by Luis Von Ahn, Manuel Blum, Nicholas
J. Hopper (all of Carnegie Mellon University, and John Langford (then of IBM). They are
challenge-response tests to ensure that the users are indeed human. The purpose
of a CAPTCHA is to block form submissions from spam bots –automated scripts
that harvest email addresses from publicly available web forms. A common kind of CAPTCHA used
on most websites requires the users to enter the string of characters that
appear in a distorted form on the screen.
CAPTCHAs are used because of the fact
that it is difficult for the computers to extract the text from such a distorted image, whereas it
is relatively easy for a human to understand the text hidden behind the
distortions. Therefore, the correct response to a CAPTCHA challenge is assumed
to come from a human and the user is permitted into the website.
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