But it does get into the "prove you're you" problem when people demand photo ID for a use name that is not the same as that on your legal ID -- which I've encountered when paying on the door, not just as security on pickup of pre-reg. Pity the name on my photo ID is the one nobody in fandom can remember even when they know what it is (as in, some of my closest friends can't remember it, including the one who has the same surname...).