They do hire (rent space to?) someone to do photographs of people at the Con, most of whom I've seen getting their photos done are in their garb/costumes. The studio they hire is local to the Bay Area. Not sure it would be feasible for me, not sure it wouldn't, and pretty sure the population wouldn't support the competition (i.e. two photographers doing the same thing same place same time).

Photography as an art form, not simply in the sci fi/fantasy venue, runs into the same situation - is it art? Come on, it's photography, anyone can take a photo.