Hold the phone! as my ol' Dad used to say.
Let's revisit this.
First of all Wert, in fact there were two Photographic Reproduction proofs in the November Brigham auction, though not the Albert. They were The E3 Special Delivery and the C5 Air Mail. Estimates were $1000 and $750 respectively.
Brigham described them as 'Printer's Composite Design Review & Approval Proof'. Quite a mouthful.
Secondly, look what I found! Purchased a box of covers last night at stamp club, and this was inside. A photographic reproduction of the 1898 Xmas stamp. The cropping of the image is similar to those in the Brigham catalogue. And comparing it to the actual stamp, some of the details are a little cruder, especially the 'rope' border.

Now I don't know if this is a proof, there's no writing or description, but I think it's interesting. Mine has half tone dots (it is not continuous tone, like a picture in your granny's photo album). Half tone dots, or a screen, are what they use in magazines etc to get graduated tones. Look at a black and white or colour picture in a book or magazine and you'll see them.
I don't know if the printers proofs usually have half tone dots, but maybe some expert out there has seen one up close.
In the end I know there's probably no way to prove this is one of those proofs, but I will certainly do some digging.
Goes to show, you never know what you'll get for 5 bucks!