Open Source Text Image such as Captcha?

I am hoping someone here might know a good open source solution for the prevention of bots?

Our programmer prefers not to work with Captcha and would like the most control possible ov开发者_JAVA技巧er it.

Could someone recommend please some good open source solutions and/or a good approach at protecting ourselves from bots?

Thank you!

You dont' mention your programming language, but for Java have a look a JCaptcha:

http://jcaptcha.sourceforge.net/