(though I'm not sure how they'll be able to scan your ID as they're kicking you out).
Well, first off when they approach you to kick you out, usually one of the first things they'll do is ask to see your id. But then they don't need even need too, the bouncer gets a good description of you as (s)he is escorting you to the curb, aproximate height, weight, hair/skin/eye colour, distinguishing facial marks, etc. Then scans through the database checking pictures they captured when you came in, like right from the front of the license, if they haven't paid to get access to a copy of the once from the dmv, untill they find you. Then welcome to the distributed black list. Vegas casinos do some of the same types of things.