This conception of the NPG may still be widespread in the public mind, as even Martin Parr thought his work would be an ill-fit for a contemporary exhibition along these lines. “I never thought of myself as a portrait photographer,” he says, “and when I first met Phillip Prodger [NPG’s former head of photographs], I told him I had only a few celebrity portraits. I just put a lightbox together and sent them to him, though I was quite surprised at what I had.” Prodger, however, had ot...