Copyright Protection and Appropriation Art

From the introduction to William M. Landes, Copyright Protection and Appropriation Art:

I want to examine the relationship between copyright law, borrowed images and appropriation art. As the term suggests, appropriation art borrows common images from advertising, the mass media and elsewhere, places them in new contexts and, thereby, aims to change the way we think about these images. Some appropriation art, such as Duchamp's use of found objects, doesn't implicate copyright at all. But when the borrowed image is copyrighted, appropriation art risks infringing the rights of the copyright owner.