Copyright protects any work of authorship that is expressed in a tangible medium of expression, is original, and has the least bit of creativity.
Copyright law (US Code 17 Section 102a) lists the following types of work:
Copyright law (US Code 17 Section 102b) does not protect the following:
Copyright act does not protect any idea, procedure, process, system, method of operation, concept, principle, or discovery, regardless of the form in which it is described, explained, illustrated, or embodied in an original work.
Copyright law does not protect ideas and facts that are included in a work.
Works in the public domain are not protected and therefore can be used without obtaining permission.
A chart to identify if a work is in the public domain is available from Cornell University.
A collection of public domain resources is available from Washington State University
Fair use provides an exception to the exclusive rights of the copyright owner and works covered by fair use may be copied without the permission of the copyright owner.