CAPTCHA Based on The Form of Letters

Abstract

The internet has been playing an increasingly influential role in human daily life, with the availability of many web services such as email, search engines and social media such as Facebook, Twitter, and Snapchat. However, these are often threatened by attacks from computer programs such as bots.  To address this issue, CAPTCHA (Completely Automated Public Turing Test to Tell Computers and Humans Apart) was developed to distinguish between computer programs and human users. One of simplest CAPTCHA is Text CAPTCHA where characters with some noise are presented to the user to type these characters where he could do that but the bot programs cannot. In spite of the fact that this system offers great security and limits of confinement programmed enrollment to web administrations, Text CAPTCHA has a few weaknesses which enable programmers to reach the mechanism of the CAPTCHA. This paper presents an improved Text CAPTCHA method based on the form of Letters.