He argued his point with the photograph he took for graffiti artist Sickboy. Sickboy uses the image on his promotional material. He claims that his creativity arises from the way he takes the photograph. In this instance the girls add to the image as it depicts how audiences interact with the image. Is this an artform? The graffiti artists would say not. They claim that he is cashing in on others art and using the fact that the art is illegal and they can't make money from it to cash in himself.
However, the street artists are aware that they produce art that can't make money and will be removed, so is it fair for them to scrutinise people taking photos if it is in such a public place? Probably not, even if those photos make the photographer money.