The New Yorker displays several iconic photographs of the civil rights movement taken by an F.B.I. informant who earned the trust of Dr. Martin Luther King Junior and his associates: “News that Ernest C. Withers, a photojournalist who documented the civil-rights movement, was also an F.B.I. informant, as reported by the Memphis Commercial Appeal over the weekend, has been met with mixed reactions from scholars, historians, and those who knew him. Throughout the fifties and sixties, Withers snapped many key moments in the South.”