The photos are in little packets, the smallest of which measure around 95mm by 65mm. Here's a sample:
These particular photos come from a packet marked: "Ostende. Hafen. 1940-11941. 10 Kriegsbilder. (Echte Fotos)". On the back, it says "10 Bromo-Fotos. Original Aufnahmen. Série No 7. Photo-Edit. J. De Meester. 4, Prinsenlaan, Oostende. Nadruk Verboden".
From this, and the caption card, it's obvious that these photos were sold during the time of the German occupation. I guess that the printer didn't manage to sell them all at the time, but managed to do so to Allied service personnel looking for memorabilia.
Unfortunately, this set is supposed to have 10 photos in it but number 3 is missing. They're still quite interesting, though; I think I'll hang onto them.
Oh, I don't believe they're valuable, by the way. Similar sets go for £10 on eBay.