> Anyone can give a good reference to make a content
> such as mp3, or image protected by DRM using java?
Which DRM do you want to use? Does it have a Java API?
Do you want to display the content in Java as well as "protect" it?
DRM on images is fairly pointless as computers have a print screen button. Even if that is disabled (which can not be done in Java), just use an IP KVM.