> trouser-wateringly good
lol! Nice expression.
I think most shop staff would think you were merely trying to take photographs of things they are told members of the public shouldn't be taking photos of (i.e. anything), since the vast majority won't be aware of this app, but they will of course be aware of camera phones. I've been challenged many times in shops while trying to sneak photos of Masters. (I always get my master eventually though!)