Josef Sudek, called the "Poet of Prague" lost his right arm as a soldier in WW1. The Czech government gave him a job to sell cigarettes. This was totally unacceptable to him. With great difficulty, he got himself a licence to take photographs. Remember this was before the time of miniature cameras like Leica, Contax, Pentax, Nikon, Canon etc.
So with ONE arm, he carried his 8x10 inches camera with plates/holders, and HUGE tripod, and photographed Prague. His images of Prague are simply gorgeous, full of sensitivity and feelings. Sudek is listed as one of the "greats" in photography.
So what is this story about McCurry with his tiny camera?
Yes. I do know it is possible. But do they actually use bracket to support the cam and the other hand for control dials? What if they are right-handed and it happened to be the disabled one. Am referring to using SLR situations.
So far, i have used Nikon D70, Fuji S5000 and Fuji S602 with just my right hand whenever the place is bright enough or using flash. Normally I do that in clubs shooting friends photos with my left hand holding a mug or a jug. The shape of the camera is good enough to hold with your 4 fingers and use the thumb as the trigger-finger.
For brick cameras, you can use your little (or ring) finger to trigger and with your thumb and index to hold it (again leaving your left hand free for drinks) but if you're a bit kan cheong, the camera might flip away and drop.