Lawrence Nicastro says he found the photo last year while going through storage items at his Las Vegas home.
Nicastro was running a service station in New York's borough of the Bronx when a man dropped off a Ford Sunliner convertible for repairs on New Year's Eve 1962.
When the man didn't return to pick up his car, Nicastro opened the trunk and placed the contents in storage.
Nicastro's publicist believes the photo was taken near Pyramid Lake, near Reno, in 1960. Monroe filmed "The Misfits" with Clark Gable in 1960 in Nevada.
The actress died in 1962.