This is a great idea, but I have a few concerns. First, you would want to make the stamp out of a material that is anti-bacterial, otherwise you're spreading gr

This is a great idea, but I have a few concerns. First, you would want to make the stamp out of a material that is anti-bacterial, otherwise you're spreading grease and germs from people's faces to other people's faces via the stamp. I'm also curious as to what resolution a phone touch screen can detect the pattern. Might there be cases where someone has an older phone or a phone with a crappy touch screen where this stamp just wouldn't work? Also, do you have to be connected to the internet for this to work? What happens if the user has no signal? Lastly (and not serious), your promo video of the girl buying the beer shows her using the stamp to activate a coupon, but she doesn't pay for her beers.