"Bloggers hate automated comment spammers. One way to foil these vermin is a system called CAPTCHA, which is described in Wikipedia as 'an acronym for 'completely automated public Turing test to tell computers and humans apart''--in other words, a challenge-response system designed to determine whether a site visitor is human or a bot. Here's how I implemented a CAPTCHA system for blog comments using free and open source (FOSS) command-line utilities and PHP, the Web server scripting language.
"I've implemented this system under two Linux distributions--Ubuntu Dapper Drake and CentOS 4--both running the current versions of the Apache Web server and PHP. The CLI utilities are from GNU Enscript and ImageMagick..."
