I have been pouring over copyright law recently and found this excerpt on
www.jjkaufman.com, an excellent resource for the laws regarding art and the sale of such.
"What does copyright protect?
Copyright is a form of intellectual property law that protects original works of authorship including literary, dramatic, musical, and artistic works such as poetry, novels, movies, songs, computer software and architecture. Copyright does not protect facts, ideas, systems, or methods of operation, although it may protect the way these things are expressed."
Seems like a very gray area to me. There is another topic on his site that is titled "How different is different Enough?" Worth a read.