What is reCAPTCHA? Glad you asked.

reCAPTCHA is a service that provides an image based question on all user input fields that is difficult for machines to interpret, but relatively easy for humans to read and answer. This prevents the average spam bot from being able to complete any form based input on your site. I recently implemented a reCAPTCHA system here on NOVALUG that has reduced spam comments down to 0.

reCAPTCHA is a FREE service provided by Carnegie Mellon university. Not only is it free, but each CAPTCHA image that you answer helps digitize text from books that the university is trying to digitize. There are premade modules/plugins for Drupal, Wordpress and Mediawiki that implement reCAPTCHA services on your sites, the reCAPTCHA team also provides sample php code for implementing their system on your custom site as well.