A camera at a fixed vertical height positioned above a reference plane, with an axis of a camera lens at an acute angle with respect to a perpendicular of the reference plane. One or more processors receive camera images of a multiplicity of people of unknown height and vertical axis of the images are transformed into pixel counts. The known heights of people from a known statistical distribution of heights of people are received by one or more processors and transformed to a normalized measurement of pixel counts, based in part on a focal length of the camera lens, the angle of the camera, and an objective function summing differences between pixel counts of the known heights of people and the unknown heights of people. The fixed vertical height of the camera is determined by adjusting the estimated camera height to minimize the objective function.
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