Works that are not under copyright are part of the “public domain” and can be freely copied, distributed, adapted and performed without permission from the author or the payment of royalties.
The length of copyright is usually 50 years after the death of the creator. In Canada public domain is sometimes referred to as “Life of author + 50” as a short for the actual term of copyright “Life of the author, the remainder of the calendar year in which the author died, and a period of fifty years following the end of that calendar year.”
Some types of works such as sound recordings, photographs and films may have a different length of copyright. For instance a dramatic film’s copyright lasts for 50 years after the creator’s death. For non-dramatic works (documentaries), copyright lasts for the remainder of the calendar year of publication plus 50 years. Photographs are covered by copyright for 50 years after the photograph is taken. In America some works of film and music were granted a copyright extension for upwards of 70 years.
Often there will be clear indication of public domain especially in libraries, historical archives and government archives. The following is one example:
Image from Library Archives of Canada: Métis camping on the prairies near their carts, 1858
Source: The Forks and the Battle of Seven Oaks in Manitoba history
Robert Coutts and Richard Stuart, editors. — Winnipeg : Manitoba Historical Society, 1994. — 93 p. : ill. ; 28 cm. — ISBN 0921950128. — P. 83 © Public Domain