I’ve been doing some research about rights and documentary production. The best document I’ve found is “Documentary Filmmakers’ Statement of Best Practices in Fair Use” and can be downloaded here .
The actual language of current copyright law pertaining to “fair use” is Section 107 and can be read here. As you can see, it’s shockingly vague.
A generally good source for research seems to be the “Center for the Study of the Public Domain” at Duke Law online Buy .