Discussion forum - commentary Spam Filter (kregion.cz)

Filter is implemented in PHP language, using MySQL database and GD library for generating PNG. Complete explanation you can find on root.cz (in czech).

Short explanation:

In source code you can find few questions, which determinate the box to revise and which letters according to colors are being revised. Both question and char code are randomly writen with text and PNG picture. Question can be filled in with random chars, which looks like typing error. Configuration and details are explained in source code.

Source code for download - licence GNU/GPL v2

spamfilter_en.tar.gz - 4. December 2006

Spam Filter you can try on example.