CAPTCHA !

If you ever purchased tickets online or even posted blog comments then odds are that you have used CAPTCHA (TM by Carnegie Mellon University) but did not know that the technology had a name or that a large NSA funded project is behind it.

CAPTCHA stands for "Completely Automated Public Turing test to tell Computers and Humans Apart" and is a challenge-response test used in computing to determine whether or not the user is human. The most common type of CAPTCHA displays an image containing distorted letters of a word or some sequence of letters and numbers. The user then needs to type the letters of a distorted image.

The different approaches include GIMPY , BONGO , and PIX .