I remember aircraft handlers in Dublin getting very upset when we wanted to take a pic of the Ryanair flight we had just come in on.
And we did ask as well.
generally any electrical device isnt supposed to be used from the boarding gate door to the aircraft.. such as mobile phones, cameras, mp3 players blah blah.. in the very rare chance a spark is caused when fuel vapour is in the air... ground staff are told to enforce this rule, some do so more than others... cant recall if anything has ever happened though.. more of a precaution
also some airports dont like pictures being took airside without a permit