SART 17.08 - Digital Drawing

After reviewing the Image Copyright information, particularly the 5 Famous Copyright Infringement Cases, how do you interpret Supreme Court Justice Potter Stuart's famous pronouncement "I know it when I see it,"  in relation to copyright law and fair use?

Is it possible to trademark or license something like a color?

How do look at the idea of appropriation in art, particularly in photographs and collage, but in any media? Possible artists to look at include Sigmar Polke, Marcel Duchamp & Ai Weiwei

How is Artstor different than Google Image Searching?