How can I add a ground wire?
Yes, in most steel boxes, one of the holes is threaded 10-32 (specifically) for taking a ground screw.  Sometimes it's risen above the bottom of the box so there's somewhere for the end of the screw to go.  

If you can't find it, it would be legal to drill and tap your own hole.  What you can't do is tap it any coarser than -32.  That's because regulation boxes aren't thick enough to give proper thread engagement on any coarser threads.   Obviously, sheet metal screws are Right Out. 

Also, if the yoke (metal ends) of the receptacle are bottoming out hard against the box, then you can ground through the yoke instead of having to hard-wire one.  This is not allowed if the ears are catching the wall and preventing it from bottoming out.  It is also not allowed if any insulating material is between yoke and box, like those little bits of paper or plastic that hold screws to the outlets.  So that leftover screw-catcher on the upper bolt would have to go.