CAPTCHA Posted by Edwin antony | at 8:20 AM

 CAPTCHA or Captcha (pronounced /ˈkæptʃə/) 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.

Early CAPTCHAs such as these, generated by the EZ-Gimpy program, were used on Yahoo!. However, technology was developed to read this type of CAPTCHA^[1]

A modern CAPTCHA, rather than attempting to create a distorted background and high levels of warping on the text, might focus on making segmentation difficult by adding an angled line

Another way to make segmentation difficult is to crowd symbols together. This is Yahoo!'s current CAPTCHA format. This might be difficult for some people to read, as seen in the leftmost example (is it "klopsh" or "kbpsh"?).