The Hague, Netherlands Institute for Art History (RKD)

London, The Witt & Conway Libraries

Marburg, Marburg Foto-collection (picture search engine)

New York, The Frick Art Reference Library (Photo Archive)

Paris, Frits Lugt’s Les Marques de Collections de Dessins & d’Estampes

Florence, Kunsthistorisches Institut Florence

Florence, Istituto Universitario Olandese di Storia dell’Arte (NIKI/Netherlands Institute for Art History)