In the last issue of Spiegel, there is an article by Leon Scherfig, named Manipulierte Kriegsfotos: Bilder, die lügen - Manipulated War Photos - Pictures That Lie.
In summary, some of the "documentary" photos that were circulated on the net as pictures taken recently in Gaza, are in reality old photos (from 2009) or even from far away places, such as Aleppo in Syria. Very reminiscent of the Nazi and Communist propaganda. Although the ease of publishing the lies can be nowadays equally easily detected and counteracted, there are still enough dummies that believe the propaganda.
The full article (in German) with the falsified picture examples and tweets can be viewed at:
http://www.spiegel.de/politik/ausland/fotos-aus-gaza-krieg-mit-gefaelschten-bildern-a-983689.html