Apply the Displacement filter to your design layer at 5% Horizontal and 5% Vertical. Select "Shadow.psd" as your displacement map. This will distort the design to the contours of the background (incidentally, this is also how I got my reflection to match the water in the UFO over Toronto picture). If your design is farther away, decrease the percentages (although less than 3% is barely noticeable). Or, if your image is up closer or you want a more "rugged" look to the edges, increase the percentages. Also, if the image is tilted horizontally more than vertically, you can raise the Horizontal percentage and lower the Vertical to get more of a perspective.