- their copyrights have expired; or
- the copyright owner didn’t follow certain required formalities (so they didn’t get a valid copyright); or
- the works weren’t eligible for copyright in the first place; or
- their creators dedicated them to the public domain. "
" Want to know if a specific work is in the public domain? (Or, if it's not, when it will be?) Give the copyright term calculator a spin. You'll need to provide some information about the work — for example, whether it's published or unpublished. But the calculator keeps track of which US copyright act applies to the work in question, so you don't have to. "I invite you to use this wonderful copyright calculator and share it with your students to enable to figure out works that are under public domain. Click here to try it