Please check out our new picture-based CAPTCHA, called Confident CAPTCHA: http://wordpress.org/extend/plugins/confident-captcha/
It stops bots and spam, but is extremely easy for people to use. No more deciphering warped and distorted words or letters. Now all website visitors need to do is click a few pictures to prove they're human and not a bot. There's also a mobile-optimized version.
Best of all, it can be used as an unobtrusive advertising platform, so website owners can earn additional revenue from their sites.
Check out the wordpress plugin, screenshots and other info here: http://wordpress.org/extend/plugins/confident-captcha/
A demo is available here: http://www.confidenttechnologies.com/Confident_CAPTCHA_Demo