My understanding is that the system looks for (and uses) the largest image on the page; I believe this means in its native form, not the size it may be stretched (or reduced) to. So, you would want to upload and place on the page the image you want, in the largest convenient format. If you don't want this image as large on the actual screen, try hiding it behind another image. -Phnord, who has never tried this but thinks it should work.