I would not want to be the man expected to fire that baby.
I think the Japanese had a similar weapon in WW II
I think they called it the Knee Mortar. It was meant to be wrested on the ground and aimed by hand.
I would guess that the mortar in your picture would be fired in similar fashion.
I'm not so sure. If you look closely, you'll see this "hand cannon" has both a trigger and trigger-guard. It looks to me as though it was intended to be fired like a pistol.
Whether anyone was actually crazy enough to do that... ;)