Hupka took thousands of hidden photographs of conductor Arturo Toscanini while Toscanini was leading the NBC Symphony Orchestra. The greatest of those photographs were published in the book This Was Toscanini, (1963) accompanyied by the essays of Samuel Antek, a violinist in the NBC Orchestra.
Hupka is also the author of Michelangelo: Pieta, a collection of a hundred photographs, from various angles and with different lighting, of Michelangelo's Pieta.