Replacing grounded outlets with grounded metal junction box
The ground screws do not make contact with the box. They're intended to secure a pigtail from the ground wire bundle (or a passthrough loop). On modern outlets they'll be green.

Some outlets are self-grounding. They have small tabs or wire springs behind the screw mount ears that make a positive connection. 

You can either replace your outlets with self-grounding ones, or simply attach the grounding conductor with the screws. The ground wires should still connect to the box if it's metal. That does appear to be a grounding screw hole in your photo. Be sure to use the proper screw (often 10-32 with self-cutting threads) to be legal.