Experimental study of CAPTCHA: A Security Primitive

Captcha as graphical passwords (CaRP) is one of the new security primitive based on hard AI problems which is a novel family of graphical password systems built on Captcha technology. Now a days different applications are employed for users, where only the human interaction is needed. To ensure that the response is generated only by the human one test is conducted at the time of authentication. This type of test is nothing but challenge-response test generated by developer. This avoids automated softwares to perform their actions on behalf of the user. Captcha avoids multiple user interactions which are actually not the human. Registration forms of number of email services use this scheme of Captcha to ensure that only humans have an account in their organization.