Likewise, a government publication that is in the public domain can contain copyrighted material. Having copyrighted materials in a public-domain document does not take away the material's copyright status. The 1976 Copyright Act , which provides for fair use of copyrighted materials, balanced a copyright owner's six basic rights with the users' right to create new works. It advances public interests such as education, scholarship, criticism, comment, news reporting and research. It has been interpreted as limited use not likely to deprive a copyright owner of any income.
Educational use is more favorable than commercial use.
The use of factual material is more favorable than the use of fictional material. The amount of material used should be small and not include the heart of the work. The greater the market effect on the original work, the less likelihood the use is fair. The narrow line between fair use and infringing use is determined in court, and all four factors are judged equally. Get permission before using material repeatedly if there is any question on the fair use of an item.