Has any photograph ever changed the course of a war? It is a claim as old as photography itself, expressing a profound faith in the power of the image to communicate and move. However, like most religious statements, it does not stand up to rational scrutiny. It relies on the coincidence of two highly improbable phenomena. First, it assumes that everybody sees the photograph in question. This was a more contingent possibility in the analogue age, and it is even less certain in our image-saturated times. Second, and more problematically, it insists that everybody has (roughly) the same reaction to the image, a conjecture betraying a blissful ignorance of human psychology.