It is, everyone agrees, a beautiful picture. The subject, Erno Nussenzweig, is an 84-year-old retired diamond merchant who lives on a quiet block in Union City and spends his days reading the Torah. The photographer, Philip-Lorca diCorcia, has filled some of the world's top galleries with his work and also has published several books. Four years ago, their worlds unwittingly collided in Times Square, when diCorcia discreetly photographed Nussenzweig, who was wearing a black, wide-brimmed hat and buttoned overcoat. It is a simple but haunting picture. The photo went into a book that has since sold out, and diCorcia has...