Sir Apollo
that can be helped.
I don't know much about GIMP but I know about Photoshop.
if the image is only pencil I suggest before taking the photo you 1.) trace it with pen or 2.) make a second copy with pen.
preferably black ink.
take the picture where the lighting seems to be even on all sides of the room or take the picture outside in a porch or under a tree. This insures lighting on all sides and it's not to bright because your under something. (make sure the sun is out lol.)
Never take it a picture with flash on. That makes the middle part of the drawing/painting to light and hard to see.
best thing I'd suggest in the long run is to get a wacom digital art pad or any other tablet. it's less of a hassle and it should be compatible with GIMP and Photoshop.
wink
Making the light as even as possible (maybe a few desk lamps) could fix the problem entirely, or at least make anything you try much easier. Highly recommended...