Heading toward the jump you are leaning forward like a jockey. If this horse was to stop you would be over it's head so fast. Sit up, and control the horse instead of rushing it towards it. Stretch your heels down and your leg. Your leg is way too crunched, and you are really just an obtrusive passenger. You are way ahead of your horses motion, and as the horse starts to jump you are way over the front of the saddle, standing in your stirrups, pinching with your knee, and allowing your leg to slip back. You are throwing your whole weight forward onto your horse's forehand. (this makes jumping hard for the horse). Take a step back, get some lessons before you kill yourself going over the fences.
I can't tell if you are wearing a helmet, but if you aren't.... please wear one.
And please, pick up your horse some carrots and apples and give it a big pat for taking care of you and being a saint for going over this with you.
Edit: thought it was you riding. But if this is your friend and your horse, you need to take some responsibility and not let your friend do something dangerous on your horse. Besides him going to get hurt, he can sue you for it, since YOU would be help liable.