All good points. I posted the PDF but should have quoted, “it is not possible to extend the length of protection for a copyrighted work by creating a derivativ

All good points. I posted the PDF but should have quoted, “it is not possible to extend the length of protection for a copyrighted work by creating a derivative.” But, I get your point: is it possible to practically extend a copyrighted work by defending a carefully-chosen derivative? I was surprised how broad this can go: the Copyright Act of 1976, 17 U.S.C. Section 101: A "derivative work" is a work based upon one or more preexisting works, such as a translation, musical arrangement, dramatization, fictionalization, motion picture version, sound recording, art reproduction, abridgment, condensation, or any other form in which a work may be recast, transformed, or adapted. A work consisting of editorial revisions, annotations, elaborations, or other modifications which, as a whole, represent an original work of authorship, is a "derivative work." So, it appears I’m not clarifying anything. But, maybe we look at the things which are not derivative works. Let’s say a movie shows a copyrighted picture on the wall. There seems to be a six-second convention beyond which a production assistant would typically obtain permission. The Titanic story comes to mind: James Cameron paid for a particular painting shown in Titanic. It was re-released in 3D and he was asked to pay again. So, within the industry, his derivative work enjoys protection, but insider copyright agreements do not survive the derivation. https://news.ycombinator.com/item?id=3890204 https://news.ycombinator.com/item?id=3890204 https://archive.ph/VF2AR https://archive.ph/VF2AR