extend:
Extending simplecaptcha is done through implementing an interface. Since configuration is done through the servlet definition in web.xml you can create your own configuration keys there and they will be propagated to your class.
The defaultCaptcha implementation will get the properties object from the sevlet and will try to load the custom classes. If this fails it will load the default implementation. The custom classes will get the properties object either in the construcotor or through a setter. So you will have to implement both.
customizing the background.
customizing the captcha chars or dictionary
customizing the distortion algorithms or
gimpy engine.
customizing the word rendering.
If you want here is the uml thing:
