I just had felt in love with this work. Alberto really shocked me.
Just with the simple first/quick look at the work, you think "not bad, not bad" but then you suddenly realize of the glass cup with water. You see the photograph is not the photograph itself, the photograph is inside the water and in my modest opinion with great mastery. Not just taking care of every detail on the whole composition but getting a greatly balanced work in which no detail makes the others decrease on importance. Also, i think there's "bonus points" on the light measurement/capture and the game between the 2 different proportions/positions of the hand.
So, i think you don't have to keep on guessing what Escher would had be doing if he had been making photographs in case of drawing