Berkeley Law Releases Public Domain Handbook

L.H.O.O.Q. (1919). Derivative work by the Dadaist Marcel Duchamp based on the Mona Lisa.

From their website:

The Samuelson Clinic is excited to release a handbook, “Is it in the Public Domain?,” and accompanying visuals.  These educational tools help users to evaluate the copyright status of a work created in the United States between January 1, 1923 and December 31, 1977—those works that were created before today’s 1976 Copyright Act.