If someone posts a home video to YouTube, and I want to use a snippet of it in a commercial video, would doing so constitute a copyright violation even if they haven’t in any way claimed their rights to it? (i.e. a © or some creative commons thing)
It would be a copyright violation. Because according to Congress, everything produced after 1985 is automatically copyrighted to its creator whether or not they stick the little © on it or make any other explicit claim to it. How do I know? Because Ze Frank Told me So.