At BHX last year I got yelled at by a young ground staff lady for taking a photo of my 6 year old grandson with the nose of the Dash-8 (which we had just disembarked from) as background. I did this without causing an obstruction or leaving the designated pax walkway. Her tone was so rude that I just told her not to be so rude and so ridiculous.
I think lack of training and strict rules / regulations can cause ground staff to act like this. Generally they're barely earning more than minimum wage in ****e conditions and working horrible hours. Sadly I know from experience that they're usually accountable for anything that happens to passengers on the ramp and usually suspended until it's been investigated, even if it was nothing to do with them and wasn't preventable.
Personally, I was never specifically told during training if photos were allowed on the ramp or not, and how to deal with passengers who may start taking photos on the ramp. As I said in my previous post, I tend to use my common sense and let them get along with it unless they're causing a problem.