Countering Spam Robots

CAPTCHAs are employed on websites to differentiate between human users and bot programs that indulge in spamming and other fraudulent activities. With the advent and advancement of sophisticated computer programs to break CAPTCHAs, it has become imperative to continuously evolve the CAPTCHA schemes in order to keep the Internet network and website free of congestion and spam-bots. In light of these developments concerning information security, in this chapter, the authors introduce the novel concept of Scrambled CAPTCHA, which is a combination of OCR-based and Picture CAPTCHAs and exploits an inherent characteristic of human vision and perception. They also introduce Hindi CAPTCHA, developed in Hindi language (Devanagari script). This CAPTCHA will typically address spamming on Indian websites. It also contributes to the digitalization of books written in this script. The authors also discuss the features and security aspects of these schemes in detail, which, to the best their knowledge, had not been implemented earlier.