Captcha Plugins for Rails

you have tow option to install captcha
for spam control

1) recaptcha plugin
this is use the http://recaptcha.net/ service get catcha image,
http://github.com/ambethia/c/tree/master

also its a great way to help translate scaned old books

2) simple captcha plugin
http://expressica.com/simple_captcha/

this is uses RMagick lib to generate catcha image