In reply to Jeff Chandler.

In all cases, you need to properly determine what is GPL code, and what is non-GPL assets, before you fork anything. Look at Debian's version of Firefox, IceWeasel, because while the Firefox code is GPL -- the Firefox name, logo, and trade dress are most certainly not.

Your fork should remove sample content if its unique, it should remove all art assets that you don't have a license to use and put placeholders or GPL/CC/PD images in their place, and it should have the documentation rewritten (preferably in a clean room environment without tainting from original copyrighted works) so that if someone DMCAs you, you can respond to the complaint with your assertion on why your project does not infringe in their IP and they can pound sand.