This PHP script provides a very user-friendly CAPTCHA solution.
You can easily embed it into your <form> generation scripts to
prevent spam-bot access.
It strives to be accessible and implements an arithmetic riddle
as alternative for visually impaired users. It does not require
cookies, but makes use of "AJAX" to give users visual feedback
for solving the CAPTCHA. It grants access fuzzily (when single
letters were outguessed) instead of frustrating people. And it
can be customized rather easily.