Comparative Analysis of CAPTCHA Based Techniques: A Review

CAPTCHA(Completely Automatic Public Turing test to tell Computers and Humans Apart ) is used by every website on the internet to prevent unauthorized user or bots to use the bandwidth and resources of the network. At the present time every user has to register on the website to access any type of information or resources so he/she has to pass the CAPTCHA test. If the user has passed the CAPTCHA test he/she is assumed to be legitimate user and can access resources or information from that site otherwise he/she is attacker or bots. So due to more attack on the web sites CAPTCHA is used to prevent these attacks. This is more popular technique used in present scenario. This paper focus on the scope of CAPTCHA,various types of CAPTCHA and its techniques.