I've been playing with the Terragen freeware program a bit and created the pictures below. You can almost get photo realism but I think that this is probably dependent on available memory during the rendering process. I have a gigabyte of ram and the rendering process takes almost 3 minutes for an 800 x 600 picture with realism set at 99%. The pictures below are basically the same setting with variations in sun position. In the extreme right I changed the viewpoint just ever so slightly.
Now, if I can just figure out how to add grass, plants, and trees!