Thumbnails are absolutely infringing... but they are fair use in most cases! Edit: on second thought, they might not even be derivative works (as a derivative

Thumbnails are absolutely infringing... but they are fair use in most cases! Edit: on second thought, they might not even be derivative works (as a derivative work requires the same spark of creativity necessary for a copyrightable work), just outright reproduction. But the point that they are fair use still stands.