“This spring, the Worcester Art Museum … will put the complex process of identifying a Leonardo at the heart of a new exhibition. The Mystery of Worcester’s Leonardo (10 March-3 June) makes the case that a work that has been in the museum’s collection since 1940, A Miracle of Saint Donatus of Arezzo (around 1479-85), should be credited to the Renaissance master.” Judith H. Dobrzynski reports.