Hans Knecht, Swiss, 1913-1986.
Hans Knecht is a bit of a mystery man. His entry on Wikipedia is short enough to be a Tweet. Even photos of him are hard to find.
What we do know is that he was Swiss Road Race Champion on three occasions and World Road Race Champion in 1946, with the event held in Zürich, his home town.
The date of this photo is also unclear. On the front it has a label saying 'Vel' d'Hiv 1947' - meaning Velodrome d'Hiver (in Paris) in 1947. On the back it says 'Knecht à Paris 21 Nov 46'.
I believe that Hans Knecht won his World Road Race Championship using a Super Champion Tour de France derailleur.
I like the expressions on the faces on the group of spivvy geezers in the background. Perhaps they have come to the cycling for a short break from trading black-market cigarettes.