Under the current law, copyright usually expires 70 years after the death of the author, or for anonymous works, 70 years from the date of publication. Crown copyright expires 50 years after publication. ... Anonymous works and photographs created before 1955 are no longer under copyright.
All works published in the United States before 1923 are in the public domain. Works published after 1922, but before 1978 are protected for 95 years from the date of publication. If the work was created, but not published, before 1978, the copyright lasts for the life of the author plus 70 years.