and if you do crop and paste, be sure to remove more than is necessary (crop a square containing the rider or a rough outline with some background) so you can line it up with the background image and then remove around the edges until you feel it is right. This also helps keep the shot looking more natural because you don't have missing lines, you don't have to erase right up to the body, and the small details (snow flying from the skis etc) can usually stay in the shot