The teaser that was shown at SDCC showed Ultron's head, and it looked very much like Ultron appears in the comics. I've got to think that this mask is probably just a mockup for the purposes of lighting reference for principle photography. Remember all of those behind the scenes videos for the making of the Star Wars prequels? You may recall seeing someone walking around the set with this globe on a stick. It was used for very much the same purposes.