It looks to me like the grounding is provided solely by that little strip of copper wire at the "bottom" screw.
Is this a safe, sane thing people actually do? I am using metal boxes with romex, with the ground wire from the romex connected directly to the metal box.
It would be helpful to me if I can rely on this automatic grounding because I am installing 2-gang boxes, each with two outlets, and many of them have an outgoing line to feed another downstream box (e.g. if you manually ground the outlets, I have to connect the incoming ground + outgoing ground + metal box + 2 outlets, it gets to be troublesome to securely connect them all and fit everything in the box).