Collectors may be born every day, but for some it can take years to discover exactly what they are meant to collect. For Peter Cohen that moment of discovery came in 1990 at a small flea market in New York’s Chelsea neighborhood. “While waiting for someone, I saw a plastic bin of snapshots that had been torn out of family albums,” he says. Without quite knowing why, he purchased five. The batch cost him eight dollars. “I came home and just looked at them,” he recalls. Since that day, Cohen has built one of the world’s largest private collections of amateur, or vernacular, photography. Although he says he’s “never even attempted to count” his holdings, he estimates he owns more than 35,000 of these largely anonymous photographs, a collection augmented by earlier purchases of Pop art prints, contemporary works on paper, and fine-art photography. Much of Cohen’s collection is stored in red, black, and orange canvas boxes stacked high in his West Village loft. Each is labeled with a specific yet openended category, such as “Couples,” “Christmas Trees,” and “Landscapes.” Inside the boxes, small photographs are protected by plastic sleeves. Some date from as early as 1890 — two years after George Eastman marketed the first rudimentary box camera, the Kodak #1, to a mass audience.

An investment manager by trade, Cohen, 65, began collecting art while a student at American University, in Washington, D.C. Over the next 15 years, he acquired a significant number of prints by the likes of Roy Lichtenstein, Robert Rauschenberg (including what is perhaps the only Rauschenberg composition featuring the artist’s own visage), and Jasper Johns. The Pop prints still claim a place in Cohen’s heart — and his home: They hang, salon-style, on a kitchen wall.

Before he was smitten with vernacular photography, Cohen collected photogravures from Camera Work, the quarterly journal published by Alfred Stieglitz from 1903 to 1917. A wistful Baron de Meyer photograph of a man leaning against a doorway, titled Teddie and printed in Camera Work in 1912, hangs near Cohen’s own front door. He also owns several self-published books by Ed Ruscha, one of the pioneers of the artist’s-book genre.

Cohen approaches amateur photography with the zeal of a new convert, despite the fact that he’s been collecting it for more than 20 years. The snapshots have become something of an obsession, he admits. The collection is the product of some 40 weekends each year spent scouring flea markets and specialist galleries for images that catch his eye. Add to that countless evenings spent on eBay. “There are a huge number of collectors,” Cohen says, “who just collect one or two themes—girls with dogs, boys with bikes, snapshots from a particular year. I buy a wide range of pictures because I like the images. If I look through 50 photographs, there will be 50 different reasons why I like them.”

Over time, Cohen began to organize his massive holdings by theme, even making little booklets on individual subjects with reproductions. He has compiled a group of photographs taken through car windows that is reminiscent of Lee Friedlander’s “America by Car” series (though Cohen notes that most of his pictures predate Friedlander’s effort, which was initiated in the late 1990s), and another of double exposures. The grouping “Dangerous Women,” originally assembled as a gift for his sister, features photographs of glamorous females toting guns, bows and arrows, and other weapons. One delightful photograph from the 1910s shows two women standing proudly on either side of a hanging alligator.