I asked this very question to the head of airfield operations at the airport that I currently work. My response to this was pax can take pictures anywhere in the airport/airfield so long as:
1) it's not at securoty, border control, customs and
2) pax are not taking pictures of sensitive areas eg fuel farmers etc (possible terrorism survey lance).
I work for an airline as a aircraft dispatcher and often get groups posing for pics at gates, on the ramp and a/c stairs. I often take the pictures for them. I have experienced colleagues and cabin crew shout at pax to stop taking pictures because of "security!". As mentioned as long as it is not in and of sensitive areas, I don't see a problem and so does my airport authority.