What does “public domain” mean?
A work in the public domain can be used without permission from the copyright owner and without paying copyright royalties. The phrase ”public domain” is a copyright term referring to works that belong to the public.
Works can be in the public domain for a variety of reasons. One is because the term of copyright protection has expired. Copyright protection has a set time limit. When the time ends, the work falls into the public domain.
Works then belong to the public and anyone may use them without permission or the payment of royalties. The term of copyright protection for photographs taken before 1955 has accordingly expired, regardless of whether the author has since died or is still alive and are available for use in the public domain.