Security Images in PHP (Captchas)

Learn how to create a sign-up form for a website with a security image / captcha. The image prevents fake sign-ups and spam. The following tutorials show how to create a security image and put it in use.

http://www.devshed.com/c/a/PHP/Security-Images-in-PHP/

http://www.sitepoint.com/article/toughen-forms-security-image