How to CAPTCHA?

Web forms are vulnerable to abuse. An automated agent can create hundreds of logins. Some web services like Yahoo! have implemented a new way to stop this. A dynamically generated image (with some obfuscation) is shown and the user enters the text as he sees it in a form text item. This is validated every time an account gets created. These images are not easily recognizable by a computer program that may maliciously try to simulate a human requesting a userid.

Try ImageMagick at http://www.imagemagick.com. This is a set of open source libraries in C, Perl, Java, PHP, VB and other languages which can be run as a CGI script as /make_image?key.