Google Google reCAPTCHA is a free service that protects your website from spam and abuse. reCAPTCHA uses an advanced risk analysis engine and adaptive CAPTCHAs to prevent automated software from engaging in abusive activities on your site. It does this while letting your valid users pass through with ease.
This job involved modifying a highly customised French Joomla/VirtueMart website for a web design agency.
Very good provider.