I often do derivative works of sketches that I like on deviantArt, the problem is convincing the original artists to allow me to make such a work. Not many artists understand Creative Commons licenses and this is such a shame, even though CC is available on deviantArt submissions. (although not Public Domain, much to my chagrin)
So here is my recent work: It’s a scene from Going Postal by Terry Pratchett , a book which is being mae into a live action film like The Colour of Magic, The Light Fantastic and Hogfather.