In this age of the web, authors and artists will invariably run into copyright issues, either in terms of their own work or in terms of fair use of another’s work. We have an obligation to make ourselves aware of the limitations imposed by copyright law and exceptions for “fair use” for educational purposes.
Stanford University library site covers all things related to copyright.
Here are two other good articles describing fair use:
A Photo Editor’s article on photo use on blogs
Carolyn E. Wright’s blog Photo Attorney, “The Fuss About Fair Use”