Outsider art

In an article on The Conversation prompted by the defacing of a new Banksy, legal scholars Mark Thomas and Samantha Pegg leave aside the tired old question of whether graffiti is art, and instead consider rather more interesting ones. Who owns graffiti - the artist, the owner of the structure on which it's displayed or the local community? Is graffiti criminal damage if it actually increases rather than decreases the value of the property? And if graffiti is itself criminal damage, can it be criminally damaged?