1. An attribute-assigning image-processing system comprising: a distributed computing system that includes multiple computer systems, each having one or more processors, one or more memories, one or more mass-storage devices, and one or more network interconnections; an input-image memory for receiving an input image provided by one or more of the multiple computer systems; a set of first-level feature detectors, provided by one or more of the multiple computer systems, that detect face-containing subimages within the input image and, for each face-containing subimage, generate a set of normalized regions; a set of second-level feature detectors that generate a set of feature vectors from each normalized region; a set of attribute classifiers that each outputs an attribute value and associated probability; and a controller that submits the input image to the first-level feature detectors in order to generate sets of normalized regions for each face-containing subimage in the input image; submits each set of normalized regions to generate a set of feature vectors; and submits subsets of feature vectors to each attribute classifier in an ordered list of attribute classifiers to assign attributes to each face-containing subimage.