Ivette Spradlin’s Instagram page is filled to the brim with images of people in masks posed in front of colorful and creative-looking homes, their gaze fixed on the photographer who takes their picture from at least 6 feet away.

Elliott Erwitt left his rented room at the downtown Pittsburgh YMCA in the fall of 1950, cameras in hand. The 22-year-old photographer walked up either Forbes or Fifth Avenue, documenting the people and...