This article from Wired raises an interesting question: once you've purchased a copy of a film, what are your rights to watch it?

At play is the question of whether ClearPlay, Family Shield Technologies, and Trilogy Studios can produce hardware and software that modifies the playback of movies (legally bought on DVD) to remove "offensive" content (language, nudity, violence, etc).

The claim of the studios is that the companies in question are creating derivative works without appropriate authorization.