No posing in Greek museums

I encountered a strange rule in the Athens National Archaeological Museum (and other Greek museums like the one in Fira/Thira): no posing allowed in front of the statues or collection. You are not allowed to take photos of a statue or museum item while someone is also visible on the photo. This rule is enforced strictly and the guards will shoot “No Posing!” when they do not like it.
Before contemplating on the reasons for having such a rule, let me show you some illegal photos:
 
Zeus or Poseidon of Artemis

 
Greek philosophers (check out how the left statue is keeping an eye on things)
The reason for the “no posing” rule is not clear. Perhaps they want to stop tourists from imititating the statue’s pose.  Some people say that the statues are considered holy and therefore you should not take photos of them.