He points to the island’s first flag, the Revolutionary Flag of Lares, which was designed ahead of a major uprising in Lares, Puerto Rico, in 1868 against the island’s first colonizer, Spain.

That image and 59 other black-and-white shots are part of “Picturing Puerto Rico Under the American Flag: The Photographs of Louise Rosskam 1937-1948,” an exhibit that runs May 11 to July 21 ...