In a phone interview, Mr. Schiller, 80, whose name was often stripped from the photo as it spread across the internet, described what he remembered of the relationship between the two actresses. He said that Ms. Fisher, who was 6 years old at the time, seemed content to sit and stare at her mother for hours.

“Her daughter was really mesmerized by her mother always,” he said. “That’s what really stood out.”

He said he had noticed the quality early on, when he was taking portraits of Ms. Reynolds at her home on Sunset Boulevard in Beverly Hills. Ms. Fisher would sit in the corner and watch as he took picture after picture, he said.

In Las Vegas, where Ms. Reynolds was performing at the Riviera Hotel, Mr. Schiller said he saw that dynamic crystallized: As Ms. Reynolds took the stage, someone who was watching over Ms. Fisher brought a stool to the wing. Ms. Fisher clambered up on top of it “all by herself,” he said, and sat through the entire performance.

Ms. Reynolds began performing a “singing-dancing act” at the Riviera in the early 1960s. By 1966, she would regularly perform seven nights a week at the venue over the course of a month and a half, according to a Los Angeles Times article from that year.

“You’re waiting for the moment in which something you’ve seen is illustrated,” Mr. Schiller said. “And then you don’t even stop and think. The image is there and your camera is like a sponge to absorb the moment.”