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this is a bright one, and probably easy to match due to really good even skin tones so i think matching colors and luminance will show how close you are more easily.  basically i think the people are about as close to 3d looking as you can get real people, so the non-shader aspects of matching reality won't hit the eye as much. http://www.renderosity.com/mod/gallery/index.php?image_id=1680385