Copyright and Fair Use policies can appear complicated--and many of them are. Essentially, Copyright laws protect authors and creators from others taking and using their works without permission. Copyright (definition) is automatically granted to the authors of original works.
(Image source: Wikipedia)
There are some exceptions to copyrights that allow access to copyright-protected materials for educational purposes. For instance, Fair Use allows instructors and students to incorporate media into projects and instruction even without permission from the copyright holder as long as you use correct citation and follow these guidelines:
Fair use guidelines apply in any educational setting but online teachers also need to follow the guidelines in the TEACH (Technology Education and Copyright Harmonization) Act. Basically, the TEACH Act says that the instructor should take precautions to ensure that materials are only distributed to students in their course.
You may have already heard about Creative Commons. It's a growing movement that allows creators to easily remove some or all of the constraints that copyright and fair use guidelines have placed on those wanting to reuse, redistribute, revise, or remix their work.
The Creative Commons website contains a lot of information that you can explore. The following information will point you to specific information from their website and highlight some additional resources.
(Image source: Creative Commons)