Most U.S. genealogists have been told that all books and other documents published PRIOR to 1923 are in the public domain. In other words, those books are not under copyright. However, that rule is changing. Starting on New Year’s Day, published in 1923 are now in the public domain. The new rule will be: all books and other documents published PRIOR to 1924 are in the public domain.
That rule will add another year again every January 1st thereafter.
Details may be found an an article by Glenn Fleishman in the Smithsonian Magazine at http://bit.ly/2rLF58a.