The present disclosure includes, among other things, systems, methods and program products applying a plurality of low-level feature detectors to an image where each low-level feature detector produces a respective low-level feature vector that represents a detection result. The low-level feature vectors are provided to a plurality of higher-level feature detectors where each higher-level feature detector produces a respective higher-level feature vector that represents a detection result based on a distribution of features in one or more of the low-level feature vectors. The higher-level feature vectors are then provided to a classifier in order to classify a human-action in the image.