Copyright Attributions Best Practice for attribution: https://wiki.creativecommons.org/wiki/Best_practices_for_attribution Creative Commons: https://creativecommons.org/licenses/by-sa/3.0/de/deed.de Subject Title Author Source License Kölner Dom & Skyline Im Abendrot Diezin Wikimedia Commons - https://commons .wikimedia.org/w iki/File:2014-09- 23%2621323020 13-10- 07%26184515_ Kölner_Dom_%2 6_Skyline_Im_A bendrot.Jpg CC BY-SA 3.0 DE - https://creativeco mmons.org/licen ses/by- sa/3.0/de/deed.e n Unknown Unknown Unknown Unknown Unknown Unknown Unknown Unknown No attribution required Hohenzollern- brücke Kölner Dom Thomas Wolf Wikimedia Commons - https://commons .wikimedia.org/w iki/Köln#/media/ CC BY-SA 3.0