Works in the public domain are generally those published before 1923. This applies to any type of work in any medium. You can freely use any work in the public domain in your courses. There are some other kinds of works that are considered public domain, such as anything produced by the U.S. Government.
A common myth is that ANYTHING on the web is public domain. This is NOT the case--websites are protected under copyright law in the same way any other text-based items are, such as ebooks, ejournals, etc.
Rickman Library seeks to support faculty and others in the university community by providing guidelines regarding copyright and the application of fair use in the academic environment, including classroom teaching, scholarship, and curriculum development.
To that end, Rickman Library:
What Is Copyright?
If you can see it, read it, hear it, or watch it, it’s probably protected by copyright law! Currently, any of the above items are automatically protected, whether or not the creator sought copyright protection or not. Items published prior to March 1, 1989 are protected by copyright if they have the © symbol. Items published prior to 1923 are in the public domain and therefore NOT subject to copyright protection.