1. An occlusion detection system, comprising: a decomposer configured to decompose an image into a set of hierarchical parts; a hierarchy of classifiers, including multiple view-based classifiers, employed to detect features in the image and the hierarchical parts; and at least one logical operation configured to logically combine a classification result from at least two of the classifiers to detect an occlusion state of the image by detennining that no face is detected in an image that has a detected person.