HIP is abbreviation of Human Interactive Proofs and is applied to call systems in which human user proves their membership in a special group through a challenge/response protocol. Some examples are: human versus machine, user himself versus any other person, adult human versus a child, etc.
HIP methods are mostly used to tell human and machine apart and are called CAPTCHA (Completely Automatic Public Turing Test to Tell Computer and Human Apart).
In this website there are some of our projects about HIP and CAPTCHA.