I think Cannonmn is spot on with Rebel, not Reber. As to precisely what it is, I will go as far as to say what it reminds me of and that is one of those Rebel large bore howitzers which ended up at Rockett's Landing in Richmond at the end of the war. First of all, it doesn't look like any photo of a Brooke gun that I have ever seen, although you can see what looks like familiar reinforcing bands. However, they are thinner than any Brooke bands that I have seen and less wide too. I believe it is a Confederate government ordered siege howitzer prototype, probably made by Anderson's Foundry in Richmond. Just look at that muzzle. Does that look like a production model to anybody?
A production model of a very similar gun is one of the large bore howitzers that were photographed at Rockett's in 1865. courtesy of LOC, via Old Photo, this image was chopped long ago from a larger view which showed 4 or 5 such howitzers from 32 pdr. (6.4") to 68 Pdr. (8") to get a larger single cannon image for the stereoscopic view. These were not Brooke guns either.