Writing in the New York Times, Randy Kennedy reports on a court decision that would make it illegal to use most work of others still under copyright as the basis for new works which "transform" the original link here.

"The decision, by Judge Deborah A. Batts, set off alarm bells throughout Chelsea and in museums across America that show contemporary art. At the heart of the case, which Mr. Prince is now appealing, is the principle called fair use, a kind of door in the bulwark of copyright protections. It gives artists (or anyone for that matter) the ability to use someone else's material for certain purposes, especially if the result transforms the thing used or as Judge Pierre N. Leval described it in an influential 1990 law review article, if the new thing "adds value to the original" so that society as a whole is culturally enriched by it. In the most famous test of the principle, the Supreme Court in 1994 found a possibility of fair use by the group 2 Live Crew in its sampling of parts of Roy Orbison's "Oh Pretty Woman" for the sake of one form of added value, parody."

There is lots more in the article about what is allowable as being legally transformative. The line between what is not allowed will remain in dispute until copyright is once again shortened to a reasonable period. I would argue that anything more that 10 years is excessive because the present discounted value of the income stream arising therefrom approaches zero and no longer constitutes an incentive to create as required by the constitution for copyright.