“I can't believe photography exists,” she exclaimed. “It seems so incredible to me that a moment can be captured—that I can show up 50 years later and pick up an image and have this emotional response. It feels like someone is whispering to me across the decades. Sometimes, it almost feels like I can whisper back.”

* * *

The origins of snapshot collecting are unclear, however, as a collector myself, judging by price increases of old photographs at flea markets and online, the phenomenon is growing rapidly. Once the domain of hobbyists, the practice has recently begun to enter the art world, with some starting to consider snapshots to be found objects in the tradition of Marcel Duchamp. That was the perspective taken by the National Gallery in Washington in 2007 when it exhibited the collection of Robert E. Jackson. More recently, in 2014, the Swann Gallery of New York conducted the first sale of found photographs by a major art dealer.

One of the attendees of that auction was Dan Lenchner. I met the collector and catering-company owner sometime later in his sprawling Manhattan apartment. We sat at his dining room table studying a standard studio portrait—a group of 12 taken in Łódź, Poland circa 1935. Only, we knew—as the sitters never could have—that in 10 years, everyone in the photo would be dead. Everyone except the man in the back row, second from the right. In the picture, he already seems separate from them—he is the only one not looking into the lens. It is a portrait of a Jewish family. It is also, inversely, a portrait of the Holocaust—a documentation of what was lost.

The man in the back row is Dan Lenchner’s father. “One of the ironies,” the son noted, “is that my father didn’t get along with his family. Even before the war, he was not a happy man. He never found himself.”

The ancestral portrait was passed down as an heirloom, but to Lenchner, it is also a collectable—one of 15,000 other images that he has bought over the years. The 70-year-old has published several books of found photographs, displaying them in pairs intended to evoke specific connections between disparate subjects: a prisoner and a baby, kids with toy guns and a wounded soldier, a woman in a hijab, and a woman in a catcher’s mask.

Among these, as among all snapshots, there is a broader connection too. Walker describes it as a shared relationship to time. “Every person in a photo is older than when that photo was taken,” she elaborated. “I look at a photo and I know someone is probably dead and that one day I'll be dead too. There must be some secret of time held in these images. I can’t help thinking that if I just study them hard enough, I'll finally be able to understand it.”

Several years ago at the New York Hell’s Kitchen flea market, Noel Buscemi, a snapshot vendor who has since passed away himself, made a similar remark to me. “Pretty much everyone in these pictures is dead,” he commented, “along with everyone who ever cared about them.” He waved a hand over his wares, strewn haphazardly in boxes like mounds of autumn leaves. The snapshots had been torn out of context. Whatever they had once meant to their former owners had vanished.