Duchamp's urinal was art once he put it in a gallery. In fact, one working definition of art is anything that is in a gallery.

Art and society was a lot more subject to sexism 50 years ago than it is now. Since that period, there have been plenty of very good female painters, 2006 Turner Prize-winner Tomma Abts among them. How much history needs to pass before an artist is called 'great'? That is the real question.

Street art is designed to be seen out of the corner of your eye, on the hoof. Art that's made for galleries is made to be looked at in a more static way for a longer period of time and may not be so striking immediately, but perhaps resonates for a longer period.