Some other helpful guides:
"Prelinger Library," via Flickr Creative Commons
“Archival Survival: The Fundamentals of Using Film Archives and Stock Footage Libraries“: A step-by-step guide for finding and acquiring material by the archivist and filmmaker, Rick Prelinger, who founded the Prelinger Archives, a collection of more than 60,000 “ephemeral” (advertising, educational, industrial, and amateur) films.
“A Primer on Researching Moving Image and Audio Collections”: A publication of the Moving Image Collections that aims to “provide guidelines, resources and encouragement for anyone—student, teacher, researcher—interested in using moving images and audio collections.”
And so, happy hunting!