I agree with the others about your legs being too far forward (aka "chair seated").
You also can work on this by riding with no stirrups. Your "gripping" power should come from your thighs; not the stirrups. The ideal goal is to have your heel, hip, and ear in a straight line.
Also, I noticed that your toes are turned outward quite a bit. Try putting what weight you do have in your stirrups to the outside part of the ball of your foot (and not the inside). This will help to turn your toes in a bit so that your feet are more parallel with your horse. Because I bet if you drop your stirrups and ride without them, your toes probably aren't turned out as much, because you haven't got a bunch of weight in the wrong place in the stirrups.
Other than that, I don't see too much else in this one "silly" picture.
∞•*˚ Βгįťţαňγ ˚*•∞
It is not enough to know how to ride; one must know how to fall.