Shadows over the rock work? Yes. Look at the position of the diver. There should be some shadows caused by him over the live rock. Also, take a look at the dimensions of the tank with the guy standing in front of it. You stated that the tank would need to be eight feet cubed. The tank sure as heck isn't eight feet tall. Assuming the man is six feet, that tank is four feet tall at most. It looks to be roughly six or seven feet wide, which would require it to be almost twenty-one feet deep (within the wall might I add) to achieve 4000 gallons.
I'm not trying to flame your post, it just looks ludicrous to claim that tank is 4000 gallons.
Edit: Looking again at the picture, it is possible that the tank is covered in parts by the masonry, but why would someone go through the trouble and expense of a 4000 gallon tank, only to make the majority of it unviewable?