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."
to share – to copy, distribute and transmit the work
to remix – to adapt the work
Under the following conditions:
attribution – You must give appropriate credit, provide a link to the license, and indicate if changes were made. You may do so in any reasonable manner, but not in any way that suggests the licensor endorses you or your use.
share alike – If you remix, transform, or build upon the material, you must distribute your contributions under the same or compatible license as the original.