A Review on Evolution of various CAPTCHA in the field of Web Security

Abstract

CAPTCHA (Completely Automated Public Turing test to tell Computers and Humans Apart) which is a security challenge through which human and bots intervention can be measured. It is a type of turing test through which programmed intervention can be detected by it behavior or solving the problem. There are various CAPTCHA problems available such as distorted string, picture recognition, audio, math and gaming CAPTCHA. Game based problem is interactive and highly secured as compare to the other CAPTCHA. In this kind of CAPTCHA user has to solve an AI problem either by drag & drop method or click based, depending on the game. The paper is intended to review various implemented CAPTCHA and compare their weakness and security parameters. Many of the CAPTCHAs are based on click based methods where user has to identify the pictures as per its appearance and click accordingly. But this kind of CAPTCHA can be intervened by image processing techniques such as object classifier. Dragging an object to the target area is an effective way but it has to be performed or solved by an intellectual problem. If dragging an object to the target area by object recognition then system may get cracked by relay attacks. Keywords: CAPTCHA, Web Security, Game, Picture Recognition, Math CATPCHA, Image Processing, Relay Attack.