To quoth the Copyright FAQ ([[Wikipedia:Copyright FAQ]]) that Jamesday and I prepared:

Taking a work in the public domain and modifying it creates a new copyright on the work. For instance, Orson Scott Card's Homecoming series is a re-telling of the book of Mormon. The books in that series are copyrighted.

However, the new work must be different from the original in order for a new copyright to apply, as the court ruled in Bridgeman Art Library v Corel Corporation (http://www.law.cornell.edu/copyright/cases/36_FSupp2d_191.htm). The Bridgeman Art Library had made photographic reproductions of famous works of art from museums around the world (works already in the public domain.) The Corel Corporation used those reproductions for an educational CD-ROM without paying Bridgeman. Bridgeman claimed copyright infringement. The Court ruled that reproductions of images in the public domain are not protected by copyright if the reproductions are slavish or lacking in originality. In their opinion, the Court noted: "There is little doubt that many photographs, probably the overwhelming majority, reflect at least the modest amount of originality required for copyright protection.... But 'slavish copying', although doubtless requiring technical skill and effort, does not qualify." [1]

--Mark