A photographer I've followed for a while now is the Canadian Jeff Wall, whose large scale images of mundane subjects regularly command prices of several hundred thousand pounds.  He has an exhibition on at the White Cube Mason's Yard at the moment (and for the avoidance of doubt this shot is not one of the exhibits).  I was expecting to leave the gallery imbued with a desire to shoot something of my own and print it at a similar size, but instead I felt somewhat confused about what makes a photograph worth exhibiting.