http://www.deutschefotothek.de/cms/gebuehren.xml states: "Free of charge are our digital objects provided by the Deutsche Fotothek (reduced quality) - they are licensed under the Creative Commons License CC-BY-SA 3.0 . You are allowed to reproduce and distribute the content, to adapt and build upon the material for different purposes, as long as you credit the SLUB as source and license your new creations under the identical terms."