“The term “public domain” refers to creative materials that are not protected by intellectual property laws such as copyright, trademark, or patent laws. The public owns these works, not an individual author or artist. Anyone can use a public domain work without obtaining permission, but no one can ever own it.
An important wrinkle to understand about public domain material is that, while each work belongs to the public, collections of public domain works may be protected by copyright. If, for example, someone has collected public domain images in a book or on a website, the collection as a whole may be protectable even though individual images are not. You are free to copy and use individual images but copying and distributing the complete collection may infringe what is known as the “collective works” copyright. Collections of public domain material will be protected if the person who created it has used creativity in the choices and organization of the public domain material. This usually involves some unique selection process, for example, a poetry scholar compiling a book—The Greatest Poems of e.e. cummings.
There are four common ways that works arrive in the public domain:
the copyright has expired
the copyright owner failed to follow copyright renewal rules
the copyright owner deliberately places it in the public domain, known as “dedication,” or
copyright law does not protect this type of work….”