spies taking pictures of spies taking pictures of spies taking pictures of spies

Some members of the Alied Forces in Germany were allowed to move pretty much freely throughout most parts of Germany - including the GDR. These military missions and other members of NATO nations inside the GDR were always hunted by the Stasi.

But what is the point of spies taking pictures of each other? Both are clearly aware of the presence of the other side so the amount of informations gathered through these images is very questionable.