I create an image with PIL:
I need to fill in the empty space (depicted as black). I coul
Depending on how you're deploying this application, another option might be to use the Gimp's python interface to do the image manipulation.
The doc page I linked to is oriented more towards writing GIMP plugins in python, rather than interacting with a background gimp instance from a python app, but I'm pretty sure that's also possible (it's been a while since I played with the gimp/python interface, I'm a little hazy).