There is a captcha script. Almost Russian written (site and help was in Russian). Library - GD. It looks like distorted letters in MultiWave.
The letters of the same color, the color is generated automatically, in the specified range. The same garbage with the background.
I lost the link to the script, I just can not find it.
Who understood what I mean, please reply =)
PS the rest of the captcha are also welcome, if they work on the site directly (ReCaptcha, with all due respect, goes through the forest), but are not the answer to the question.
PPS script was free