Sampling has long been an area of contention from a legal perspective. Early sampling artists simply used portions of other artists' recordings, without permission; once hip hop and other music incorporating samples began to make significant money, the original artists began to take legal action, claiming copyright infringement. Some sampling artists fought back, claiming their samples were fair use (a legal doctrine in the USA that is not universal). International sampling is governed by agreements such as the Berne Convention for the Protection of Literary and Artistic Works and the WIPO Copyright and Performances and Phonograms Treaties Implementation Act. Today, most major artists obtain prior authorization to use samples, a process known as "clearing," by gaining permission to use the sample and, usually, paying an upfront fee and/or a cut of the royalties to the original artist. Independent musicians, lacking the funds and legal assistance to clear samples, are at a disadvantage unless they seek the services of a professional sample replay company or producer. Recently, the free culture movement, started mainly by Lawrence Lessig, has prompted many audio works to be licensed under a Creative Commons license that allows for legal sampling of the work provided the resulting work(s) are licensed under the same terms. Usually cases of alleged plagiarism are settled out of court, due to the expense of litigation. Most artists try and settle for costs that will be less than defending costs. Since the 1850s federal courts have published fewer than 100 opinions dealing with this issue. The Columbia Law School Library's Music Plagiarism Project provides information on many cases over the decades, with a few dating back to the 19th century. Led Zeppelin has been successfully and unsuccessfully accused of music plagiarism several times. The following are accusations of plagiarism appearing in notable media:   The truth is, I seriously doubt that there is any negative intent there. And a lot of rock & roll songs sound alike. Ask Chuck Berry. The Strokes took "American Girl" [for their song "Last Nite"], and I saw an interview with them where they actually admitted it. That made me laugh out loud. I was like, "OK, good for you." It doesn’t bother me.