The image of the Material Girl, who often cast herself as a sort of latter-day Monroe, appeared in "Sex," her 1992 book of risque photography. In it, she posed in heels and handbag, with a cigarette in her mouth.
Lawrence Nicastro, 73, said he found the grainy, poster-size photo last year while going through storage items at his home in Las Vegas. He believed it had been left by a customer at his service station in the Bronx in 1962.
Nicastro and his wife, Phyllis, said they had spent about four months researching the origin of the photograph and called in Chris Harris, a publicist and Monroe expert, for help authenticating it.
Harris said it was a dead ringer for Monroe and scheduled a Wednesday news conference to unveil the image to reporters.
The two men gave The Associated Press a sneak peak Tuesday.
"You're right; it's Madonna," Harris said after being told of the mix-up. Harris said he believed someone had slipped the poster into Nicastro's storage as a prank.
"If there ever was an embarrassing moment," he said, adding that he planned to go ahead with the news conference to "face the music."
There is one person, he noted, who should feel good about the mistaken identity.
"Who wins here? Madonna, of course," Harris said. "She really looks like Marilyn Monroe."
