I think asking who wants out instead of asking who wants in is weirder now than I would have thought a couple years ago. Since then I have started doing research with human subjects. In many countries, including America, researchers are expected to get informed consent before collecting data from people in their studies, even though the published studies hide identifying information.
Getting informed consent from the players at a larp doesn't seem like too difficult a task. Unless a player is under 18, then getting informed consent becomes difficult.
Still, if an organization plans to use someone's picture in a publication, I think the right thing to do is to make sure the person knows what's going on and is cool with their image being used.