From the US Copyright Office
"One of the rights accorded to the owner of copyright is the right to reproduce or to authorize others to reproduce the work in copies or phonorecords. This right is subject to certain limitations found in sections 107 through 118 of the copyright law (title 17, U. S. Code). One of the more important limitations is the doctrine of “fair use.” The doctrine of fair use has developed through a substantial number of court decisions over the years and has been codified in section 107 of the copyright law.
Section 107 contains a list of the various purposes for which the reproduction of a particular work may be considered fair, such as criticism, comment, news reporting, teaching, scholarship, and research. Section 107 also sets out four factors to be considered in determining whether or not a particular use is fair:
The distinction between fair use and infringement may be unclear and not easily defined. There is no specific number of words, lines, or notes that may safely be taken without permission.
Acknowledging the source of the copyrighted material does not substitute for obtaining permission."
Use of images, videos, and audio by individuals for educational purposes is generally considered fair use. Additionally, the library licenses many materials (such as those linked elsewhere on this guide) and specifically includes clauses allowing use in USC's educational environments. If an image, video, or audio is used for publication (of some sort) then users need to receive approval from the creators or owners before use to avoid copyright law violation.