How to break CAPTCHA?

Question

What are the methods, algorithms used to break CAPTCHA ?

Answer 1

The Security Now Podcast has an episode about this. Link to transcript follows.

http://www.grc.com/sn/sn-101.txt

Update, better links:

http://www.grc.com/sn/notes-101.htm http://www.grc.com/sn/sn-101.htm

Answer 2

Depends on how rudimentary.

My friend was working on some captcha stuff, and sometimes the simplistic ones could be broken by applying filters and then passed into an OCR.

e.g. Edge filter -> OCR.