It is an anonymous or pseudonymous work and 50 years have passed since the date of its publication
It is a posthumous work and 70 years have passed since the date of its publication
It is another kind of work, and 70 years have passed since the year of death of the author (or last-surviving author)
It is one of "official documents (laws, resolutions, decisions, and etc.), as well as their formal translations; official symbols and marks (flags, emblems, orders, banknotes, and etc.); works of popular art"
This work is in the public domain in the United States because it meets three requirements:
it was first published outside the United States (and not published in the U.S. within 30 days),
it was first published before 1 March 1989 without copyright notice or before 1964 without copyright renewal or before the source country established copyright relations with the United States,
it was in the public domain in its home country on the URAA date (January 1, 1996 for most countries).
For background information, see the explanations on Non-U.S. copyrights. Note: This tag should not be used for sound recordings.