Metal box grounding question GFCI outlet
That is what is called a “bootleg ground” and it’s both against code and dangerous. This can be done when there is no ground in the box. It works because the ground and neutral are connected back in the main panel. However, there are problems, such as if the neutral wire back to the panel fails, suddenly, the outlet ground is at 120 volts (through the load, out the neutral pin, through the wire to the ground pin.
The interesting thing is that it appears that the wires are going through conduit which should provide a good ground to the metal box.
Assuming that the box is indeed grounded, all you need is to install a “self grounding” GFCI.
On the other hand, if the box is not grounded, what you must do is install a GFCI, leaving the ground screw disconnected. Also, label the front of the outlet “no ground”. There should be a label in the packaging that you can stick on.
A GFCI is the only legal way to install a 3-prong outlet on an ungrounded circuit.