@RedGiant is this the actual "scan" file CGC gave you? I always thought they actually scanned them but I guess not. The corner edges are too jagged to not be photoshopped. I'm a graphic designer and use photoshop pretty much daily. The white areas on the outside of the slab are made up of PURE white, also pointing to an alteration.
If I had to guess on their setup, I think CGC has a studio setup with a camera mounted to a frame, pointing down, with lots of indirect lighting to cut down on glare. They then take that photograph and put it into photoshop, likely using a re-used layer mask that is the size of the CGC case. They fill the rest of the area with white on the edges (already part of the mask). They then edit the levels while looking at the actual book to compare the actual book to the "scan" image - at least that's what I'd do to maintain fairly accurate consistency. If their camera is setup with a good white balance then they may be able to skip the last step.