Whoever photoshopped this did a *very* good job! The skin tones, the angles of the faces and the lighting on the faces match and both sets of eyes are looking in the same and proper direction.
The reasons I think the picture is photoshopped is because when I looked at it zoomed, Mamoru's collar and neck on his right side lookes blurred compared to the left side which is sharp and clear. It looks like the artist used the "clone" and "blur" tools there to erase something from the original picture - maybe the original model's hair or even his chin if his face was at a different angle. Also, when zoomed in on Mamrou's head, there are intermittent single pixle lines of real/bright/solid white where his hair curves/zigzags.
I could be totally wrong, but for what it's worth, that's what I think.
Holy frekking crap! That is a CUTE picture! (yes, it is sprite time)
I always thought Shibby's head looked a little big for his body cuz he had a skinny little twink body. That shot looks genuine enough for me, but who knows. Maybe it's just wishful thinking on my part.