Cary Bass wrote:

After speaking with a Swiss German user--he seems to be under the
impression that "pd" stands for "Pressdokumentation"; literally "Press
documentation" or "Press kit" as we commonly refer to it in the US.

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Yes, that context would be more reasonable since other pictures on this website (as far as I have checked them) have e.g. ''Reuters'' instead of ''pd'' (http://www.nzz.ch/nachrichten/international/suedafrikas_praesident_bietet_armee_auf_1.739334.html). And Reuters definitely is not a licence, but the source/author.

Cecil