CAPTCHA alternatives

If your web forms are getting spammed, and CAPTCHA isn’t a good solution, here are some possible alternatives. 
 
 http://isc.sans.org/diary.html?storyid=1836 	 http://softwareas.com/captcha-alternatives-and-end-user-attitudes 	 I’ve taken to renaming our feedback pages, and then using robots.txt to prevent search engines from indexing their new names. 
 
 Related Link: https://kb.ucla.edu/link/438 
 
 The Akismet service has a good reputation, and is widely used by Wordpress amongst others. It could be another layer of protection against spam. 
 
 
 http://akismet.com/ (official site) 	 
 http://codex.wordpress.org/Akismet (an example of it in a blogcentric CMS ) 
 
 Jared Smith of WebAIM has compiled a series of server-side processing techniques that get rid of spam without the use of CAPTCHA . Scripts are provided in PHP . 
 Spam-Free Accessible Forms 
 The scripts include: 
 
 Detect spam-like content within submitted form elements 	 Detect content within a hidden form element 	 Validate the submitted form values 	 Search for the same content in multiple form elements 	 Generate dynamic content to ensure the form is submitted within a specific time window or by the same user 	 Create a multi-stage form or form verification page 	 Ensure the form is posted from your server