How to break CAPTCHA ?

What are the methods, algorithms used to break CAPTCHA ?

From stackoverflow DFG

• 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

  From magnifico

• Duplicate: Has reCaptcha been cracked / hacked / OCR’d / defeated / broken?

  From cletus

• 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.

  From Calyth