For their latest campaign, promoting Burger King’s one dollar menu, ad agency Crispin Porter + Bogusky chose to break the mold of former AR campaigns. First, there’s no mini-site, the whole experience is neatly contained within a single banner ad. Moreover, there’s no need to print a marker. You simply show this ad a one dollar bill and it shows you an item from BK’s one dollar menu. You flip the bill and it shows you another item. Finally, when you hide the bill from your web cam, your face is covered by a king’s mask.
Apparently it works with other bills and even white sheets of paper, so you can give it a try. The banner is featured over here.