What an astounding collection and I can see how one photo postcard (with front and back visible) can launch an entire story. Here‘s a great book which mentions some of the folk photographers that are probably among Sante’s collection. I am not a curator of photography, but think calling these postcards “folk photo postcards” works very well:
See Google Books for: Real photo postcard guide: the people's photography
By Robert Bogdan, Todd Weseloh