Harry Benson won notice photographing the Beatles on their first American tour, then soon after became a legend in his own right. Although Scottish by birth, Benson’s career is part of American history: he’s photographed every president since Eisenhower, marched with Dr. King, was standing next to Robert Kennedy when he was assassinated, and captured Nixon’s resignation. He has embedded himself in countless wars. A survey of Benson’s 70-year career is now on display at Southampton Art Center. —Lucy Horowitz