The CAPTCHA Project.

I'm sure you have all seen images like this one. It is used to prevent computers from signing on to web sites as human users.

A CAPTCHA^TM test is a program that can generate and grade tests that:

• Most humans can pass.
• Current computer programs can't pass.

CAPTCHA stands for "Completely Automated Turing Test to Tell Computers and Humans Apart." That sounds more complex than it is. A CAPTCHA is a computer generated image that contains distorted and often overlapping words. The idea, of course, is to read the words. Since this is hard for computers to do, computers can't pass the test. But since a computer generated the image, it can tell whether the submitted answers are correct. Click the image to go to the (surprisingly primitive) CAPTCHA page, which generates a new image (more complex than the above) whenever you refresh the page.