In this digital world; security is an important concern towards access control management that can be done through some kind of turing test i.e. CAPTCHA. The term CAPTCHA was introduced for classifying credibility of user whether the intervention has been initiated by human or bots. . CAPTCHA stands for “Completely Automated Public Turing test to tell Computers and Humans Apart”. It is a protection tool that denies junk or bots entries in the way of challenging bots with a problem. CAPTCHA has been represented in various forms such as distorted strings, 3D CAPTCHA, picture recognition CAPTCHA, Gaming CAPTCHA and many more. The conventional CAPTCHA is in the form of distorted string where user will have to recognize the same. The recent approach is gaming CAPTCHA and most of the game may increases the server load towards the browser. The logic behind the gaming CAPTCHA is dealing with dragging & dropping object to the target position, so these CAPTCHAsdo not belong to the hard AI problems. The motive of this paper is to review few existing CAPTCHA techniques that challenges bots claiming better testing in the field of web security.

CAPTCHA, Web Security, Turing Test, Gaming CAPTCHA, 3D CAPTCHA, Picture Recognition CAPTCHA

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