1. A computer-implemented method comprising: selecting exemplars based on an image, the exemplars taken from example images as examples of an object that is detectable in each example image; grouping the selected exemplars into at least a first subset of exemplars and a second subset of exemplars; extracting features from multiple regions of the image; applying each exemplar in the first subset of exemplars to the features extracted from the multiple regions of the image to detect object candidate regions; extracting additional features from the object candidate regions; and applying each exemplar in the first subset of exemplars and the second subset of exemplars to the features and the additional features extracted from the object candidate regions to validate one or more of the object candidate regions.