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