If you got the images from a GPLed app or game, there's no reason for you to assume that you are free to redistribute those images or create derivatives of them, as they may be under a different license.
Good point, that didn't occur to me. Happy Sammy should clarify whether the images are explicitly licensed under GPL or whether they were just included with a game whose code was GPL, in which case there would be no automatic right to do anything with the images.
(Posted 4 minutes ago)
Check this:
www.gnu.org/licenses/gpl-faq.html#GPLInProprietarySystem
Check this:
www.gnu.org/licenses/gpl-faq.html#GPLInProprietarySystem
Free as in speech, not free as in beer. To (mis?)quote FlameDuck's old sig.