Ken Van Sickle will never forget the day in 1955 when he became a photographer. He was in Paris, where he’d moved shortly after finishing his military service in Korea, to study painting. One day in the Luxembourg Gardens, while sketching with a friend, he had an epiphany.

“My friend said, ‘Your painting isn’t that good, but your photography really is,’” Mr. Van Sickle, 87, recalled. “I almost immediately understood he was right.”

Mr. Van Sickle soon gave up painting and began seriously pursuing photography instead. Over the next year, he shot about 60 rolls of film in bars and cafes, at parties and clubs and in streets and parks. As he developed his photographic sensibility, he formed a portrait of the kind of artistic, carefree life that has long drawn expats to the City of Light.