Two examples of material in the public domain are United States government works and writings for which their copyright has expired. Generally anything published before 1923 cannot have copyright protection and is in the public domain.<ref>http://www.copyright.cornell.edu/training/Hirtle_Public_Domain.htm</ref> | Two examples of material in the public domain are United States government works and writings for which their copyright has expired. Generally anything published before 1923 cannot have copyright protection and is in the public domain.<ref>http://www.copyright.cornell.edu/training/Hirtle_Public_Domain.htm</ref> |