Secure CAPTCHA Generation

Abstract

Digital media becomes an effective way of communication which is available round the clock to everyone including humans and machines. This put the requirement for machines to differentiate between human and machine as far as access of the website or its relevant services is concerned. CAPTCHA (Completely Automated Public Turing test to tell Computer and Human Apart) is a test that helps machines (or programs) to differentiate between human and machine. CAPTCHA should be easy for users to solve and difficult for bots to attack. A simple and efficient text-based CAPTCHA verification scheme is proposed which is easy for human and hard for bots. The proposed work uses virtual keyboard, eliminates input-box, and does verification on the basis of the positions of the characters. The work is extended by using handwritten characters in the virtual keyboard and randomizing the positions of the CAPTCHA and keyboard. Response time analysis of both types of virtual keyboards and machine has been performed and results are discussed.