commons-captcha 
A Java servlet for generating simple captcha images.
Unlike other Captcha generators, this generator asks the user to click on a certain character, instead of typing a text.
This software is part of the Shredzone Commons.
Documentation
See the online documentation.
Contribute
- Fork the Source code at GitHub. Feel free to send pull requests.
- Found a bug? File a bug report!
License
commons-captcha is open source software. The source code is distributed under the terms of GNU Lesser General Public License Version 3.