Fair Use provides protection from copyright infringement for certain types of use, including research, teaching, commentary, parody, and reporting. However, these terms depend on a multitude of factors, many of which may be unclear, and can always be contested in court. This page offers suggested websites to find CC licensed work that is clearly labeled and optimal for reuse in your own projects.
Creative Commons has a search tool specifically for finding CC licensed work across multiple websites: CC Search
Here is a list of other places to find CC-licensed multimedia.