As well as being the author of a number of books on art history, throughout his career he has been credited with identifications of several "lost" works by Baroque and Renaissance painters, including a disputed identification of "Apollo the Luteplayer" by Caravaggio and "Madonna and Child with the Infant Saint John the Baptist" by Andrea del Sarto. In 2007 Whitfield's gallery removed a loan of paintings from the New York gallery Salander-O'Reilly a few hours before the opening of a major exhibition of old master paintings, due to concerns over the "uncertain legal situation" confronting the New York gallery.