The public domain consists of creative works that have no owner and are free for all to use. There are several ways things are in the public domain. One is that they are not eligible for copyright or were not copyrighted. Another is that they were once copyrighted but the copyright has now expired. A third class includes works of the United States Government that are in the public domain by law. The laws and court decisions of the state governments are also in the public domain.
When something is in the public domain, you do not have to get permission or pay a licensing fee to use a work in any way you want. You can do anything you like with it. You can reprint a book. You can record a song. You can put a photograph on t-shirts. You can make a movie of a play. You can put a poem on greeting cards.
Cornell University's Copyright Information Center has created a useful chart to determine whether a work is in the public domain. U.C. Berkeley's Samuelson Law, Technology, and Public Policy Clinic has created a handbook and flowcharts for those researching whether works are in the public domain. Duke University's Center for the Study of the Public Domain has many resources on its website.
Some works are ineligble for copyright. The Copyright Office gives these examples:
Facts are not copyrightable. The Supreme Court says "the first person to find and report a particular fact has not created the fact; he or she has merely discovered its existence [and] one who discovers a fact is not its 'maker' or 'originator.'" That requirement of originality means photographs that are simply copies of other works are not copyrightable. Nor are jokes, recipes, and the designs of clothing and fashion copyrightable. To be eligible for copyright, a work must be one of authorship and the Copyright Office has ruled that works created by nature or animals are uncopyrightable because they have no author. For example, the monkey selfie shown here, taken by a macaca who triggered the shutter on a camera left in a jungle, is not copyrightable because the animal took the photograph.
A work may never have been copyrighted. Under the current law, the Copyright Act of 1976, copyright exists immediately upon the creation of a work, but previously a work had to be registered for copyright with the Copyright Office to be protected. Until 1978, the Copyright Office published all new registrations and renewals of copyrights in the Catalog of Copyright Entries (CCE), available in the Wells Library on the tenth floor of the East Tower at Z642.A2 and in digital form here. Checking the CCE will confirm if a work was registered or renewed for copyright. The Copyright Office has published a useful guide: How to Investigate the Copyright Status of a Work.
The law formerly required a work to bear a copyright notice in English giving the year of publication and the name of the owner of the copyright. The law was strict on copyright holders' obligations to give notice exactly as the the law required and failure to put a copyright notice on a work or even putting it in the wrong place could result in the loss of copyright protection for the work. For example, under the Copyright Act of 1909, the copyright notice had to appear on the title page of a book or the back of the title page and a publisher who placed the copyright notice on the back cover forfeited his copyright.
A list of other common problems with pre-1978 copyright notices is available in the Copyright Office's part of the Code of Federal Regulations at 37 C.F.R. 202.2. These defects in a work's copyright notice could invalidate the copyright protection of a work published during the years 1923 to 1977. Failing to place a notice on works today does not affect its copyright, but it is still advisable to include a copyright notice. Doing so alerts others that the work is copyrighted and provides information regarding who to contact to reproduce or otherwise exploit the work.
Copyrights are for limited times. Until 1992, copyrights in the United States were issued for an initial term and then a renewal term. For example, the first American copyright law, the Copyright Act of 1790, provided for a fourteen year initial term renewable once for an additional fourteen years of protection. Formerly, if the copyright was not renewed, then the copyright expired after the initial term ran. Beginning in 1992, works that were still in their original term were automatically renewed. So works copyrighted from January 1, 1964 to the present are in still in copyright. Works copyrighted between January 1, 1923, and December 31, 1963, are in the public domain if the copyright was not renewed after the initial twenty-eight year copyright term. Everything published in the United States before 1923 is in the public domain because their original and renewal copyrights have expired.
An example of a work that was copyrighted and renewed but is now public domain is Harriet Beecher Stowe's novel Uncle Tom's Cabin. The novel was copyrighted on its initial publication in 1851. At the time the governing law, the Copyright Act of 1831, provided for a twenty-eight year term for copyrights which could be renewed once for a further fourteen years of copyright protection for a total of forty-two years of protection. When the original term of twenty-eight years expired in 1879, Stowe renewed the copyright for fourteen more years. When the fourteen year renewal term ran out in 1893, the book became public domain.
An example of a work that was copyrighted when first published but the owner failed to renew the copyright is the 1941 film Meet John Doe, directed by Frank Capra. The film was registered for copyright when released. Under the Copyright Act of 1909, the initial copyright was for a twenty-eight year term that expired in 1969. No renewal registration was filed so the film entered the public domain in 1969 when the original twenty-eight year term ended.
The initial registrations for copyright and renewal registrations were published until 1978 in the Catalog of Copyright Entries. The Wells Library has a set of these volumes on the tenth floor of the East Tower at Z642.A2. Links to all volumes in digitized form are available here. Iris Wildman and Rhonda Carlson's book Researching Copyright Renewal, available as an e-book, is a useful guide for how to research copyright renewals.
The laws passed by Congress and the decisions of Federal courts are in the public domain by the terms of the Copyright Act of 1976, which makes all Federal government works uncopyrightable. The Supreme Court ruled in 1888 that the decisions of state judges were uncopyrightable. Federal courts have also ruled that state and local laws are also uncopyrightable.
One of the largest producers of uncopyrightable works is the United States Government. By law, all works produced by the federal government are ineligible for copyright protection. (This does not apply to works created by state and local governments nor to those of the United Nations and its affiliated organizations, all of which may be copyrighted.) Well-known government publications such as the Congressional Record and the Federal Register are public domain. The Census Bureau's reports on the population, White House press releases, and Geological Survey maps and bulletins, are also public domain works. So are many artworks, photographs, and films commissioned by the federal government. Nearly everything published by the Government Publishing Office (known as the Government Printing Office from 1861 to 2014) will be in the public domain.
For example, the Dorothea Lange photograph at right, "Migrant Mother," is public domain because Lange took it while working for the Farm Security Administration to document the lives of farm workers. The Library of Congress has 160,000 such F.S.A. photographs available on its website. Many such collections of government-created works are available on the Library of Congress's website, such as the collection of Works Projects Administration posters and the Historic American Buildings Survey collection of architectural photographs and drawings.
One exception to this general principal is that United States Postal Service works, including the designs of postage stamps, are copyrightable. Stamps and other works created by the Postal Service's predecessor, the U.S. Post Office Department—which became the Postal Service in 1971—are in the public domain. But postal works since 1971 could be under copyright. The Postal Service's page on rights and permissions is here.