Documentation Centres
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)