What do you mean by smooth? Do you mean the motion? If you want more smooth motion, then you can select the keyframes and press F9. That make the moving smoother. But if you are talking about the image that will bounce, then you simply need the high quality image, whether it's skull or anything else. Also some images might loose quality when you down-scale them. So if the image you are suing is too large, that might ruin the quality. Hope thus help, but if I misunderstood your question, then tell me and I might be able to help. Good luck.