Just a Simple Effect I taught myself in the GIMP a long time ago, when I was first learning about graphics programs.  I would run the photocopy filter.  Then cut around the image, to delete the extraneous lines.  I'd put a layer underneath, and use one of the light effects filter (like G-Flare or supernovea), then change the blending mode of the top layer (can't remember to what, probably screen, overlay or multiply.  You can experiment).