Films, books, music, images and other creative works simply enter into the world of public property and are available to all without worrying about who owns what. Sometimes, the items are created by a government (training films, historical photos, etc.) and are- by US government definition anyway- the property of taxpayers, that is, the entire citizenry(even worldwide!) because we paid for them with our tax dollars and therefore we are the owners. The idea being since we own the government, we also own whatever that government produces, hence all US government documents are public domain (except for documents designated as secret or vital to national security).
In the US, if the work originates from the private sector, be it a commercial enterprise, an individual or other source, then the copyright cannot last more than 120 years if created after 1978. If created before that year, then it expires after 28 years unless renewed with the U.S. Copyright office. Sometimes, copyright renewal is forgotten or simply not bothered with and the work becomes part of Public Domain.
|A quick search revealed this early|
portrait of Abraham Lincoln.
(source: Private Domain!)
There's no cost and no registration required. The service is free to anyone in the world and people are encouraged to upload their own public domain creations for posterity.
It's very easy to find what you're seeking: Type in the "search" window at the top of every page and the site returns with a selection of items matching your search terms. Books, films, audio and the like each have a logo next to them to explain what format the item is in (i.e., photo). Click on the link and your desired item is in front of you for your enjoyment. By the way, software is available for download too, but you might want to beware when treading in those potentially virus infected waters.
Give the Internet Archive a try by clicking here- you might be surprised what treasure you might find.