Legality of using artwork from GPL-ed games
makecheck: Seems to be summed up by 2(b) in the GPL:    You must cause any work that you distribute or publish, that in
    whole or in part contains or is derived from the Program or any
    part thereof, to be licensed as a whole at no charge to all third
    parties under the terms of this License.

That suggests you need to GPL your application to use art from a GPL'd game.