A friend showed Pacino a 20-year-old photo in which the actor was standing next to Spector.
Pacino says he has no memory of the moment.
The movie, Phil Spector, debuts in March. It focuses on the client-lawyer relationship between Spector and Linda Kenney Baden, who represented him in his first trial on charges that he murdered actress Lana Clarkson. That ended in a mistrial, but Spector was convicted in a second trial and is now in prison.
Pacino says he didn't want to meet Spector in prison because he would be a different man than the one Pacino is portraying, who hadn't yet been convicted.
Pacino wore a dizzying array of wigs in his portrayal of the eccentric Spector, whose Wall of Sound style was an integral part of pop music in the early 1960s.
He watched video clips of Spector to help him with his portrayal. "I didn't know anything about him, except that he was responsible for a lot of great music and this strange case," Pacino said.
Dame Helen was a last-minute substitute in her role. Bette Midler had begun filming as Baden, but had to withdraw because of a bad back. The film's executive producers are Barry Levinson and David Mamet.