A Retrospect on Different side of CAPTCHA Techniques

In today’s digital world, security plays an important role in the field of web applications. CAPTCHA is a challenge reaction test that segregates human from machine based automatic program that may harm data credentials. It is required to protect the website or user data from different kind of machine attacks. To ensure the security, CAPTCHA is a tool through which a turing test can be performed that denied robots to intervene with the systems. CAPTCHA stands for Completely Automated Public Turing Test to tell Computers and Human Apart. Machine based attacks can harm the database by enrolling junk entries and an account can be hacked through brute force attack. By having these problems on mind, there are so many CAPTCHA techniques have been introduced such as text based CAPTCHA that involves 3D text, moving letters, distorted text and other than the text based CAPTCHA there are also graphical CAPTCHA, Audio CAPTCHA. One Time Password based CAPTCHA have been carried out for better security concerns. So, there are so many ideas have been developed till now which claim better security approach and the motive of this paper is to review the previously proposed systems that may have some bugs and complicated for human to solve in less time. The paper also emphasizes the proposed solution or system that replaces the existing system and provides better level of accuracy.