In addition to my college classes, I also teach on the high school level. No wonder the district tells us to not use anything that is not district purchased, in the public domain, or available via a creative commons license.

We have to remember that material is subject to copyright restrictions even if not formally on file with the government.  We need to be clear what material is in the public domain and what is not.

We as instructors find ourselves faced with the need to not merely find material that we can use with our students, but also to ensure that we do so in a manner that honors intellectual property rights.  

It is quite easy to cross boundaries into copyright infringement without intending to do so. The fat that you think that the use of material is fair does not make it "fair use", and can open both you and your institution to serios finanical ramifications/