A PHP based captcha generator.
Captchaz requires a PHP installation with GD extension and TTF font support.
It was started back in 2008 before reCaptcha and other distributed captcha generators became widely used and there was no real easy-to-use and secure captcha generators for PHP.
The background is not separated from the text in function (ie. it is not a somewhat rotated grid or waves) therefore it is harder to be distinguished by robots but still can fairly easily be read by humans - ad-hoc tests shows that after the first two-three uses it becomes much easier.
It is also not based on stretching, punching, squeezeing the words that can make really hard to be read by humans in some cases - although it might be a good security measures against the robots too (unfortunately).
So it's design principle were simplicity and portability.
If you have any comments, patches feel free to share them, I'd be more than happy to hear them!