Originally Posted by
NudgingSteel
If the airport owner, or an agent acting for them, asks you to stop, you're committing trespass.
You're trespassing if you don't stop, you mean.
Originally Posted by
750XL
Speaking as a ground pleb myself, the issue is more about using personal electronic devices within the aircraft footprint
Well not the OP's issue, he was specifically talking about taking photos on the apron.
And even on board, it's arguable whether a camera (as opposed to a phone with a camera) counts as a PED. I can't find any trace of electronics in my Box Brownie.