Jo C. Tartt Jr. regularly sells original prints by master photographers for thousands of dollars each. But some of his favorite pictures are the kind that most of his fellow art dealers would consider worthless.

Of Tartt’s collection of roughly 5,000 vintage photos, a couple hundred 19th-century images have been defaced, likely by their original owners. In some, a fine-point metal tool was used to scratch out a person’s face in a group shot; in others, paint or chemicals were applied to blot someone or something out. Was this mutilation a reaction to death? Divorce? Abandonment?

Tartt has no idea—which is one reason he’s so fascinated by these Victorian oddities. What does seem clear, he says, is that 19th-century Americans were less aggressive about analyzing visual images than we are today. To explain, he brings out an old photograph of two babies held by a person completely shrouded in a dark cloth. To modern eyes, the figure looks like a burqa-clad woman. But in a day when portraits required long exposures, the babies simply needed to be held steady for the camera. Presumably, their mother, or maybe their nanny, was trying to do so as inconspicuously as possible.

“At the time, I suspect that people would never have even noticed the figure in back,” Tartt says. “To them, it would just be a picture of two babies. The possibility that someone, someday, would think about the wider context of the picture probably never entered their minds.”

Tartt, 60, a three-decade Washingtonian who grew up in Alabama, opened a gallery on Q Street NW in 1986. Three years ago, he closed it and sold the building; for the past year, he has run his appointment-only business from an office in Dupont Circle. “I sometimes feel guilty calling this work,” he says amid the modest clutter of his second-story space on Connecticut Avenue. “I get to come in for a few hours and just play with my hobby.”

Tartt finds many of his photos, including ordinary family snapshots, at estate sales. Only a small number possess an unexpected artistic sensibility; most, he says, merely demonstrate that Americans, of all racial and ethnic backgrounds, have used casual photography to document their successes. “If you look through personal albums, you inevitably see images that are advertisements about how the family is doing well,” he says. “They have the money to buy a camera and make photos. They inevitably pose by their car and their house. They get nicely dressed and photograph their vacations. It’s a presentation of one’s domestic life to the world.” —Louis Jacobson