Genealogists often use and sometimes republish information from old documents as well as old films and photographs. We have always been told that anything published in 1922 or earlier is now in the public domain but those items published in 1923 or later might still be protected by copyright. That is about to change. On January 1, 2019, most items published in 1923 will become public domain. Anything published in 1924 will remain under copyright until the year 2020, anything published in 1925 will remain under copyright until the year 2021, and so on.
In 1998, the Sonny Bono Act changed the dates to specify that published works from 1923 to 1977 will remain under copyright for a period of 95 years. The works then become public domain on January 1st of the 96th year.
A later modification change the rules once again for works published after 1977.
You can read about the changes in an article by Glenn Fleishman in The Atlantic web site at: https://theatln.tc/2FxlfBU. Warning: It’s complicated!