The Congress shall have Power ... To promote the Progress of Science and useful Arts, by securing for limited Times to Authors and Inventors the exclusive Right to their respective Writings and Discoveries.
United States Constitution, Article I, Section 8
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Link to a University of Texas Libraries copyright crash course. Provides two versions of crash courses to take. There is links to documents, Fair Use, getting permissions, digital library, TEACH Act and many other resources.
http://guides.lib.utexas.edu/copyright
Copyright Crash Course and Georgia Harper. http://doi.org/10.15781/T24J09X6J 
Link for book Copyright and Cultural Institutions: Guidelines for digitization for U.S. libraries, archives & museums. Many useful flow charts and information. It is published under Creative Commons
Copyright Law in the United States. Link to the government Copyright Law Publication. More information on United States copyright can be found on home page at copyright.gov. It can be searched by chapters or 
appendix. https://www.copyright.gov/title17/
A few Chapters to get started in different areas of Copyright click to go directly to that chapter PDF versions available.
Works protected by federal copyright must requirements of the Copyright Act. According to The Copyright Act [17 U.S.C. §102] this list is a broad example of what can be covered.
