Designing a Secure Text-based CAPTCHA

Captcha is stands for Completely Automated Public Turing test to tell Computer and Human Apart. As the increase of automated bots systems or software that misuse and corrupt the public web services, the user must required going through and solving a Turing test problem, before they are use web services. This Turing test is called Captcha. In this paper we have discuss an improved text-based captcha which is more secure, and more robust as compared to another Captchas.