Any work published before 1923 is in the public domain, as is any work produced by an employee of the federal government in their official capacity. Works published between 1923 and 1977 generally receive copyright protection for 95 years from the date of their publication. If the work was published in 1978 or later, even if it was created before then, protection usually extends for 70 years after the author of the work dies. Distinctive rules apply to works made for hire or works that were published anonymously or under a pseudonym. Rights for these works last for 95 years from the date of publication or 120 years from the date of creation, whichever is less. (If the author’s name is eventually disclosed to the U.S. Copyright Office, the usual term of 70 years after the author’s death applies.)
Checking Copyright Renewal Records
Works that were published between 1923 and 1963 were subject to renewal requirements. You can consult the records of the U.S. Copyright Office to find out if the author failed to renew the copyright. This would mean that the work has fallen into the public domain, even if less than 95 years have passed since the date of publication. You can hire a private copyright search firm to help you check a renewal, or you can ask the Copyright Office to search the records for you at a more reasonable rate.
You can also search for copyright renewal records on your own. If you are looking for a work published in 1950 or later, you can find the renewal records at the Copyright Office website. You can find the records for works published earlier in the Catalog of Copyright Entries at the Internet Archive.
Donations to the Public Domain
A copyright owner can choose to surrender their rights in a certain work. This means that the work is released into the public domain so that anyone can use it. The owner must make an express and unambiguous statement of their intent. You should not assume that a work has been dedicated to the public domain unless it is very clear. Sometimes this occurs through a Creative Commons CC0 license, but this is not the only method.
Finding Materials Online
You should proceed carefully before assuming that you can download and use materials from the Internet that may qualify for copyright protection. You would not be able to tell whether a certain work on the Internet is covered by a copyright. Before you use the material, you should try to find the author and ask whether your use is permitted. If they are not the owner of the copyright, they can tell you whom to contact. You may be able to use a very small part of a copyrighted work without permission if you are not using it for profit or if you are using it for educational purposes. If you are not sure whether your use would meet this test, you should err on the side of caution.