1. A method comprising: applying a plurality of image filters to each of a plurality of image windows defined at a plurality of locations in a face in an image to produce a set of descriptors representing contents of each of the plurality of image windows; processing outputs of the plurality of image filters for the plurality of image windows using a feature selection stage, the feature selection stage comprising choosing a subset of the set of descriptors for each of the plurality of image windows; estimating a first relative likelihood of a predefined facial action unit occurring in each of the plurality of image windows, the first relative likelihood for each of the plurality of image windows being based on the subset of the set of descriptors for each of the plurality of image windows; and producing a facial action code score for the face for the predefined facial action unit, the facial action code score quantifying a second relative likelihood of a presence of the predefined facial action unit in the face, the quantifying comprising combining the estimated first relative likelihoods for the plurality of image windows; wherein the applying, the processing, the estimating, and the producing are performed using computer hardware.