Simple Captcha is a simple and robust CAPTCHA plugin. Its implementation requires adding up a single line in views and in controllers/models. To install Simple Captcha in your Rails 2.0+ project, use the following command:
More information and usage instructions are available at http://expressica.com/simple_captcha/.
Author: Sur Max
Installation:
ruby script/plugin install svn://rubyforge.org/var/svn/expressica/plugins/simple_captcha