  A CAPTCHA (Completely Automated Public Turing test to tell Computers and
Humans Apart) is an automatic security mechanism used to determine whether the
user is a human or a malicious computer program. It is a program that generates
and grades tests that are human solvable, but intends to be beyond the
capabilities of current computer programs. CAPTCHA should be designed to be
very easy for humans but very hard for machines. Unfortunately, the existing
CAPTCHA systems while trying to maximize the difficulty for automated programs
to pass tests by increasing distortion or noise have consequently, made it also
very difficult for potential users. To address the issue, this paper addresses
an alternative form of CAPTCHA that provides a variety of questions from
mathematical, logical and general problems which only human can understand and
answer correctly in a given time. The proposed framework supports diversity in
choosing the questions to be answered and a user-friendly framework to the
users. A user-study is also conducted to judge the performance of the developed
system with different background. The study shows the efficacy of the
implemented system with a good level of user satisfaction over traditional
CAPTCHA available today.
