I think that's Cumberbatchs character on the inside of the glass, the color of the shirt matches the same color that hes wearing when hes sitting in the captains chair.
Ha! And if thats the case have they already given away his death scene? In a reversal of Wrath of Khan it looks like Spock is the healthy one, the way he appears to be standing. It would also point to this being a kind of sympathetic villain that Spock would make this gesture for him.