Check out the digital copyright slider. The tool itself is pretty simple. You basically slide the arrow up and down the years starting from "Before 1923″. The boxes on the left (Permission Needed? and Copyright Status/Term) tell you whether a work is still copyrighted or whether it's now in the public domain, free for you to use and repurpose any way you like. Unfortunately, actually figuring out the copyright status of a work isn't so simple as dragging your mouse-most of the years seem to be marked by a fuzzy period of "Maybe".