De Desconocido – British Library: http://imagesonline.bl.uk/?service=asset&action=show_zoom_window_popup&language=en&asset=1074&location=grid&asset_list=28433,20366,20368,20369,1074,3434,7809,18284,20383,20399&basket_item_id=undefined, Dominio público, https://commons.wikimedia.org/w/index.php?curid=1664621