I just surfed across reCAPTCHA whilst researching some code for DMCMS. reCAPTCHA is a site developed to make better use of the 'Captcha' security devices utilised on most web sites. Captcha's are those pictures with distorted words that you need to type into a box to validate your submission when posting information on the web. They are used to prevent spam by trying to prevent automated scripts from posting information. The basic idea behind reCAPTCHA is that it uses Captchas to convert text scanned from books (the captcha picture) by validating and then storing the result - thus allowing books that cannot be recognised with OCR software to be converted into the digital format. A great idea!
I am currently looking into integrating reCAPTCHA into DMCMS for user comment validation