International Journal of Engineering Associates
CAPTCHA-Completely Automated Public Turing test to tell Computer and Humans Apart. CAPTCHA is used for preventing dictionary attacks against password authentication systems. Password is been used as an authentication mechanism to provide a secured access control to a system or a site. It is now almost a standard security technology, and has found widespread application in commercial websites. The most widely used CAPTCHAs rely on the sophisticated distortion of text images rendering them unrecognizable to the state of the art of pattern recognition techniques.