CAPTCHA: A Systematic Review
SHIVANI SHIVANI, Rama Krishna Challa · 2020
With the massive growth of accessing Internet-based services by users, there is a need to limit services use to human beings only rather than intelligent bots. The biggest challenge in front of researchers is to determine incoming requests are from benign users or bots. A CAPTCHA (Completely Automated Public Turing Test to tell Computers and Humans Apart) is a basic tool for preventing access to Internet-based services by intelligent bots. It plays a vital role in numerous security applications for denying automatic registration conducted by bots. This paper presents a systematic review of different types of CAPTCHAs and primarily focuses on the benefits of "text-based CAPTCHAs" over other schemes. Further, this paper highlights the major deficiencies of the text-based CAPTCHA schemes.