  Human Interactive Proofs (HIPs) are automatic reverse Turing tests designed
to distinguish between various groups of users. Completely Automatic Public
Turing test to tell Computers and Humans Apart (CAPTCHA) is a HIP system that
distinguish between humans and malicious computer programs. Many CAPTCHAs have
been proposed in the literature that text-graphical based, audio-based,
puzzle-based and mathematical questions-based. The design and implementation of
CAPTCHAs fall in the realm of Artificial Intelligence. We aim to utilize
CAPTCHAs as a tool to improve the security of Internet based applications. In
this paper we present a framework for a text-based CAPTCHA based on Devanagari
script which can exploit the difference in the reading proficiency between
humans and computer programs. Our selection of Devanagari script-based CAPTCHA
is based on the fact that it is used by a large number of Indian languages
including Hindi which is the third most spoken language. There is potential for
an exponential rise in the applications that are likely to be developed in that
script thereby making it easy to secure Indian language based applications.
