  Common and important applications of person identification occur at distances
and viewpoints in which the face is not visible or is not sufficiently resolved
to be useful. We examine body shape as a biometric across distance and
viewpoint variation. We propose an approach that combines standard object
classification networks with representations based on linguistic (word-based)
descriptions of bodies. Algorithms with and without linguistic training were
compared on their ability to identify people from body shape in images captured
across a large range of distances/views (close-range, 100m, 200m, 270m, 300m,
370m, 400m, 490m, 500m, 600m, and at elevated pitch in images taken by an
unmanned aerial vehicle [UAV]). Accuracy, as measured by identity-match ranking
and false accept errors in an open-set test, was surprisingly good. For
identity-ranking, linguistic models were more accurate for close-range images,
whereas non-linguistic models fared better at intermediary distances. Fusion of
the linguistic and non-linguistic embeddings improved performance at all, but
the farthest distance. Although the non-linguistic model yielded fewer false
accepts at all distances, fusion of the linguistic and non-linguistic models
decreased false accepts for all, but the UAV images. We conclude that
linguistic and non-linguistic representations of body shape can offer
complementary identity information for bodies that can improve identification
in applications of interest.
