PWNtcha stands for "Pretend We’re Not a Turing Computer but a Human Antagonist", as well as PWN capTCHAs. This project’s goal is to demonstrate the inefficiency of many captcha implementations.

For an overview on why visual captchas are a bad idea, see Matt May’s excellent presentation, Escape from CAPTCHA, as well as the W3C’s Inaccessibility of Visually-Oriented Anti-Robot Tests working draft.