So many of the stories Aubrey ‘Po’ Powell relates to the camera in this affectionate portrait of the art and design group Hipgnosis, which he formed with Storm Thorgerson, are deeply ingrained in rock music’s history. There are the 60 red footballs stretching out to the horizon atop Saharan desert sand dunes on The Nice’s Elegy, the offthe-wall choice of a cow to grace Atom Heart Mother and