Where would you stand from a legal point of view if the member of staff in question took offence to having his / her picture taken and asked for it to be deleted? I would think that doing something like this would be highly provocative and may increase your chances of being offloaded from the flight and thrown out of the terminal.

I have often found that asking to see the name badge of the offending member of staff and getting pen and paper out to write to down ruffles their feathers enough to want to resolve the situation for you and in the event that it doesn't you have their name and necessary details to make a complaint.