Visual events in computer vision are studied from the perspective of algebraic geometry.Given a sufficiently general curve or surface in 3-space, we consider the image or contourcurve that arises by projecting from a viewpoint. Qualitative changes in that curveoccur when the viewpoint crosses the visual event surface. We examine the componentsof this ruled surface, and observe that these coincide with the iterated singular loci ofthe coisotropic hypersurfaces associated with the original curve or surface. We deriveformulas, due to Salmon and Petitjean, for the degrees of these surfaces, and show howto compute exact representations for all visual event surfaces using algebraic methods.