1. A method to perform people metering for audience measurement, the method comprising: segmenting image frames depicting a location in which an audience is expected to be present to form a sequence of scenes; for a first scene in the sequence of scenes, identifying a first key frame representing a first sequence of image frames corresponding to the first scene; and processing the first key frame to identify an audience depicted in the first scene, wherein processing the first key frame comprises: comparing an image signature representative of the first key frame with a set of reference signatures representative of a set of reference scenes to determine a comparison result; and processing the first key frame based on the comparison result to identify the audience depicted in the first scene, wherein processing the first key frame based on the comparison result comprises: assigning the first key frame to a processing queue with a first priority when the comparison result indicates that the image signature does not match at least one reference signature in the set of reference signatures; assigning the first key frame to the processing queue with a second priority when the comparison result indicates that the image signature matches at least one reference signature in the set of reference signatures, the second priority being lower than the first priority; and using priorities associated with key frames included in the processing queue to prioritize performing processing on the key frames to identify respective audiences depicted in respective scenes represented by the key frames, the key frames including the first key frame.