There are many unanswered, hard to find answers pertaining to the legal aspects of using work in the public domain. However, the rules are really quite simple. If the work is in the public domain, you can use it however you wish to use it. The real trouble comes in determining if a work is in fact in the public domain.
However, you may use work that is in the public domain, without gaining permission from the author. If you change the work, you can become the author of it, and copyright it. If you do not change the work, you may sell it as is, but it is a good idea not to put yourself as the author of the work in this case.
Thatís pretty much it. Other than this, you are free to do as you will with public domain works. You can use part or all of a work, you can convert printed work to digital work, you can use bits and pieces of public domain music or films, you can use public domain photos however you like.
When you change a public domain work, however, and make it your own, you do need to copyright it. For instance, if you use a bunch of old photographs to create a collection of photographs that collection is copyrightable material, even though each individual picture is in the public domain. Someone can still use an individual photograph from your collection ñ but they cannot use the entire collection.
Again, the most important thing to understand and know is how to determine that a work is in fact in the public domain. That will be covered in a future article, but for now, if you are in doubt, take the time to verify that a work is in the public domain before you use it, and also make sure you understand the difference between public domain and fair use.