this is something I have currently been working/struggling with. Im finding the easiest way to do this is to make your image as simple as possible. Meaning, make the image as close to monotone as you can. Remember, highlites in the picture from reflective surfaces or the camera flash will appear as a very high elevation in Bryce (may sound a lil obvious, but its something that Ive been dealing with lately). I usually just make the image completely white and tinker with details after that, depending on the texture to make up for any lack of details in the modeling. Dunno if any of my rambling helped, but I tried :-