It's so frustrating, watching some poor neophyte try to expand an image on their iPhone, isn't it? Maybe they're new to Apple's touch-screen technology. Or maybe their hand/eye coordination/intuition is just meh. No matter! Something really genius has been created for this exact situation.
Designer Juan Sanchez has come up with an origami training-set of gestural interface motions; paper models to pinch, swipe, reverse-pinch(?), flick, etc.