You guys are at least half right; I'd left a node on that should have been off.
But it's probably not the black levels, it's that the garbage and grain and shake hide everything. As soon as you can really see the flat tone of the painting, it looks like a painting. To me the big rock on the right side is a far worse offender, but again... Apparently, George didn't like this painting either; part of why the foreground stuff was added. From a compositing standpoint, the painting's luminance is mismatched from the live plate - it would need more contrast in just the painting elements, the foliage needs a change in tone, etc. It's not a great comp, no question about it. Harrison is reviewing now.
Does this forum not autoscale images or...?