Re: the photo...
"Two hours later [after singing "Happy Birthday" to JFK in Madison Square Garden], Monroe made her entrance at a party given by theater magnate Arthur Krim. After an hour, President Kennedy pulled the actress away from the other guests and into a corner, where they were soon joined by Robert Kennedy. The three stood talking for approximately 15 minutes."
"Later the Attorney General appeared uneasy as White House journalist Merriman Smith chatted with Monroe while writing in a small notebook. When Bobby was informed by a Secret Service agent that a candid photo had been taken of Marilyn and the Kennedy brothers, his face grew stormy."
From http://www.coverups.com/monroe/countdown.htm