One important feature of a cognitive system is to perceive and understand its environment and to adapt its actions to changes and unforeseen situations. In this paper, we propose a scheme for visual surprise detection in cognitive mobile robots. With the robot's observation and a set of reference images previously acquired near its current viewpoint, a pixel-wise surprise trigger is computed using Bayesian probabilistic inference techniques. With appropriate mathematical approximations this algorithm can be implemented on modern graphics hardware which nearly allows for real-time surprise detection. In order to refer to prior observations, a mobile robot has to be able to re-localize itself with respect to its environment. Thus, we also present two online image-based homing algorithms which both facilitate the computation of location-independent surprise triggers. Experiments show acceptable results in terms of robust and fast detection of unexpected changes in the environment.