I was under the impression that unnumbered pieces from Sideshow have certificates. At least, my Red Skull which I bought from Sideshow has one. I guess those can be faked as well.
Depending on the quality of the pictures, maybe a darker tone of red would improve it. Also why is he looking up? Would prefer if he looks more downwards, gives it a bit more evil/menacing look.
Really nice custom head for Thanos. Did you contact him directly through email for one? Since I also got the custom base on my way, a custom headsculpt would make a perfect addition to the piece.