merged->make_transparent ();
for (list<PositionImage>::const_iterator i = images.begin(); i != images.end(); ++i) {
merged->alpha_blend (i->image, i->position - all.position());
merged->make_transparent ();
for (list<PositionImage>::const_iterator i = images.begin(); i != images.end(); ++i) {
merged->alpha_blend (i->image, i->position - all.position());