cre_captcha

A basic, single-file captcha library designed for flexibility, ease of use, and customizability. This library has two separate interfaces -- the traditional PHP server-side interface, and a client-oriented AJAX / JSON interface which can be called at any time. This dual interface allows you to, for example, alert the user of an incorrect answer before your server processes that giant form they have spent the last half hour working on.

There are many different settings you can customize to your liking, such as altering how the images are drawn, what kind of textual captcha to use (string-based, math-based, or word-based), the colors used in the final image, the distortion factor, and various other factors. It is designed to easily fit into any web form. You only need to worry about two functions: One to make() a new captcha, and one to check() if a user's answer is correct.