R. Heinrich (Troppau), n.d., The studio of R. Heinrich, Johannisgasse 9 Eck Schillerpark 1, Troppau, Carte de visite, back, Private collection of Fr. Gregor, LL/54053
R. Heinrich (Troppau) n.d. The studio of R. Heinrich, Johannisgasse 9 Eck Schillerpark 1, Troppau