Linda McCartney’s “Portrait of an Era,” taken during the “Sgt. Pepper” press launch, immortalized the exuberance that infused the Beatles’ music. Linda (1941 - 1998), Paul’s wife, was originally a receptionist at a magazine office who got into a Rolling Stones’ press reception and took photos that led to her employment as “Rolling Stone” magazine’s first staff photographer. Candid, spontaneous and innately perceptive, Linda’s compelling images chronicled musicians’ joy, introspection and frailties.