I have been looking all over for tutorials in how to use the GIMP (GNU Image Manipulator Project) to do lightsabre blades. The GIMP has a Hollywood cousin called Cinepaint. Both are F/OSS and run on just about any and every platform capable of doing the job. (PC+Win32, PC+Linux, Mac OS X)
I'm putting the links down here and putting down for the night but I want to play with this and show you what comes of it. I have the perfect pic to do a test with (my most recent sabre creation in its full-length pictorial debut) and it should be a piece of cake to get rid of the tell tale shadow that says "no, that isn't a real lightsabre."
Here's the GIMP tutorial for stills...
and here's the Cinepaint tutorial for video rotoscoping.