Snappers snapped

It was perhaps inevitable that the photographer's lens would eventually turn in upon itself, and group exhibition Photography on Photography takes in the results from the last 40-odd years. During the 1960s, we had Andy Warhol looking to photography as a mechanical, mass-producing medium which was in perfect synch with his Pop Art ideals. By the late 70s and early 80s, conceptual artist Sherrie Levine was upending all our notions of authorship and originality by appropriation - taking photographs of famous prints by the likes of Walker Evans and calling them her own. And now, with the digital invasion throwing up its own possibilities, these self-reflexive games look set to continue.