Another coworker of mine mentioned to me that a hobby of his was defeating CAPTCHAs, and that instant, I realized that there were two completely different routes to do that. One social, and one technological. CAPTCHAs are, of course, a Completely Automated Public Touring test to tell Computers and Humans Apart. Those squiggly letters you're forced to enter to post on a forum, register new accounts, or whatever. They make them to prevent mechanical submissions, which get really annoying, really quickly.
The technological approach is to basically reinvent OCR, Optical character Recognition. OCR has gotten a lot of funding as a way of automating the conversion of paper documents into computerized ones, to gain the advantages of computerized documents -- easy transmission, copying, editing, and so on. An OCR approach analyzes the graphical elements to determine which letter they were originally, and enters that. Supposedly, really good ones can work with just a 3-pixel row.
The social approach is to decide that only humans are capable of reading the bent and distorted letters of a CAPTCHA and convinces them to do so. One common approach is to offer something in exchange, like file downloads, or pornography. There are plenty of people who will willingly do just about anything to get more of those things, including decipher letter puzzles. It's not as fast, but it is plenty reliable. After all, the goal of the CAPTCHA maker is not technically circumvented, a human being is solving each and every one of their little puzzles. Just...not in the way they had hoped. Social attack CAPTCHA are promptly cached and used to hammer the server with mechanical submissions.
My coworker, however, said he took the technological approach. He took pride in the quality of his OCR craftsmanship, boasting on his only requiring of the right three rows to totally guess the correct answer.