Ruby/CAPTCHA

"CAPTCHA" stands for "Completely Automated Public Turing Test to Tell Computers and Humans Apart." It’s a fairly common trick on the Internet, where a website will require you to enter some text that has been jittered, rotated, and rendered against a noisy background. (Presumably, such text cannot be easily read by software, and so prevents automated agents from performing whatever action is being protected, usually registrations.)