It is no secret that CAPTCHA is not the most effective way to combat spam. But it could work for some folks. It certainly keeps inexperienced spammers at bay. Math Captcha happens to be a cool plugin that adds CAPTCHA to your login, registration, comments, and contact form on your website. You don’t have to do any programming and can hide CAPTCHA for logged in users.
Math Captcha lets you hide CAPTCHA for logged in users. Users have the option to show CAPTCHA as numbers or words. You can change title and time for your CAPTCHA fields. The plugin is ready to be translated. A pretty interesting CAPTCHA plugin all around.[via]