One case that has had a huge effect on how we understand rights to use images in the United States is the Bridgeman Art Library v. Corel Corp. case of 1999. In this case, it was decided that photographic copies of public domain images or objects could not be copyrighted. At the crux of this argument was originality. If you exactly reproduce an image of a thing, it is a copy of an original and only original works are considered copyrightable.
If we look back at another court case dealing with music, we can begin to understand the nuances of how the American legal system governs art. Art, among other things, is essentially defined as an original work—and any original work is under copyright. But Campbell v. Acuff-Rose Music was the case that determined parody was “fair use,” so anyone could use portions of other people’s original works, as long as it was only a component of another original work. It also decided that 2 Live Crew was allowed to use Roy Orbison’s “Pretty Woman” as a basis for a rap song.