Pictures are the tangible traces of our visual world. They are the materialisation of a classifiable, datable, and localizable object; a vocabulary of expressions that, when examined on a large scale, becomes key to understanding changes in visuality over time and space. This is precisely the goal of Visual Contagions, a project at the University of Geneva that aims to use computational analysis to understand what images circulate and how some of them become iconic. To achieve this goal we have developed a novel multi-scalar analysis that combines computational exploration of visual similarities with spatiotemporal classification. The method is applied to a global and diachronic corpus of illustrated periodicals, using algorithms to compa...