What do these photos have in common?

That's right, all of these photographs were taken by Parisian photographer Robert Doisneau. My friend MLL recently sent me a calendar of Doisneau photographs, which now takes pride of place on my desk, and I was wanting to share this month's photo 'le baiser du Pont des Artes' but I can't find a copy on the web - so I have decided to substitute these three instead.