...impossible. His natural talent and ability for lurking meant that he went to the precaution of being largely obscured by fencing, and was anyway so distant as to be featureless. (Or perhaps he IS featureless?)
He may even have been wearing a 'fence suit' as extra camoflage.
He was also onscreen for approximately 0.633 of a nanosecond, thereby rendering freezeframe useless. Cunning tactic for the modern lurker I thought.