On the website of the interesting hz-journal you'll find an interesting interview with Sachiko Hayashi about Sampling, Copyleft, Wikipedia, and Transformation of Authorship and Culture in Digital Media...
He reports that Marcel Duchamp introduced the idea of readymade and modern appropriation in 1919 with his "L.H.O.O.Q" hoax, "that questions the nature or definition of art itself." and introduces you to the various Topics considering sampling and copyrights...