Tracing via online resources

Online resources are also important, such as German and international provenance and image databases like ERR Einsatzstab Reichsleiter Rosenberg, Fold 3, Foto Marburg, Frits Lught, Galerie Heinemann, German Sales, Getty Research, Looted Art, Lost Art, Proveana, RKD Nederlands Instituut voor Kunstgeschiedenis, etc.