It is important for anyone involved in the creative business arena, including video professionals, to have a working knowledge of copyright law and the "fair use" exemption. For your convenience, here is the "Copyright Basics" circular from the US Copyright office. And here are additional Information Circulars and Factsheets. In addition, here is info about copyright myths. (Please note that the latter link is not an official site of the US Copyright office.) I sincerely hope that you find these links both useful and educational.