New writers—and even experienced ones—often confront the question of copyright when using quotes, song lyrics, passages from books or articles, pictures, and other created material. Penalties can be severe, so it’s a good idea to be sure what you want to use is not currently copyrighted—or to get written permission, a process that can be lengthy as well as expensive.
What IS public domain? This website defines and explains it, stressing at the end of the article that once a work is in the public domain, it is there to stay (variations excluded).
Go here for more general information on public domain.
Another good site is Copyright Term and the Public Domain in the United States(current as of January 2010)
When I was teaching and wanted to do something innovative in the classroom, I harked back to the old adage, “Better to ask forgiveness than permission.” But copyright infringement is no joke—so be careful.
If anyone finds any questionable or incorrect information here, please let me know! Or, if you'd like to share other links or personal experience, leave a comment or be a guest here at The Word Place.