I've been documenting the Brooklyn graffiti scene for the past year, and it's full of innovative artists, working in ground-breaking materials and methods. But nobody breaks the paradigm like Leeds artist Paul Curtis, who goes by the tagger alias Moose. The Moose method is to clean the walls he tags – the negative space left behind is his art. (See photo – possibly a reference to that Dylan Thomas poem?)

Authorities are debating what to do with him, as they can't exactly haul him in for cleaning without a permit. "You force people to confront whether or not they like people cleaning walls," he says, "or whether they really have a problem with personal expression."

Talk about the medium being the message.