All art and materials are copyright protected.
A Copyright is a form of protection provided by the laws of the United States to the authors of original works made by that author. Those original works include the following:
2.musical works, including any accompanying words
3.dramatic works, including any accompanying music
4.pantomimes and choreographic works
5.pictorial, graphic, and sculptural works
6.motion pictures and other audiovisual works
These categories are very broad. If those 8 categories include the items that can be Copyrighted, what isn't protected by a Copyright?
1.Works that have not been recorded (for example theatrical works that have not been put in written form)
2.Titles, names, short phrases, and slogans; familiar symbols or designs; mere variations of typographic ornamentation, lettering, or coloring; mere listings of ingredients or contents
3.Ideas, procedures, methods, systems, processes, concepts, principles, discoveries, or devices, as distinguished from a description, explanation, or illustration
4.Works consisting entirely of information that is common property and containing no original authorship (for example: standard calendars, height and weight charts, tape measures and rulers, and lists or tables taken from public documents or other common sources)
One common misconception that many have about Copyrights is that if a work does not have a Copyright notice that it is not Copyrighted, however, this is not true. As of April 1, 1989 almost all works are Copyrighted whether they have a notice or not. It is, however, beneficial to have a Copyright notice on all original works. The proper form for a Copyright notice is as follows:
Copyright [date] by [author/owner]
You can replace "Copyright" with the "C" in a circle symbol (©) but not (C).
Another common misconception is that if you make up a story based on a Copyrighted work that your story belongs to you. Copyright law is explicit that the making of works based on or derived from other Copyrighted works are the the property of the owner of the original work. You need the authors permission to use parts of another persons work. The one exception is parody. This brings in the subject of "fair use."
Fair use is a way of being able to reproduce a work without violating Copyright laws. Usually fair use is used for short commentary to criticize works by other authors (you should include as little as needed for the commentary.) It should not hurt the commercial value of the work (they would no longer need to purchase the work because they read your commentary.) Fair use isn't an exact doctrine, either. You should be careful when using it.
So, what can you reproduce? If the work is not registered and has no commercial value it receives very little protection. The author still has some rights regardless of the commercial value of the work. If you are going to violate a Copyright "because you can get away with it because the work has no value" you should ask yourself why you're doing it. In general, respecting the rights of authors to control their works is a principle worth adhering to.