Who was Ernest Withers? Most Americans may not know the name, but they do know his photographs. Withers took some of the most legendary images of the 1950s and '60s: Martin Luther King, Jr., riding a newly integrated bus in Montgomery, Alabama; Emmett Till's uncle pointing an accusatory finger across the courtroom at one of his nephew's killers; scores of African-American protestors, carrying a forest of signs reading "I am a man." But while he...