I'm really not sure... that would be tough. I understand that lots of other photographers will use the same locations, but if their whole shoot mirrored mine in terms of posing at that location, I might politely email them to say your flattered that they seem to like your style, but that you work hard at what you do... but then, I'm not really sure. Confrontation is hard and awkward. If they've only done it once, maybe let is slide, it might be a coincedence. But if they continue to do it, I'd definitely say something