1. An apparatus to count a number of persons in a monitored environment, comprising: an image sensor to collect a plurality of pixels; a pseudorandom number generator configured to generate sets of pseudorandom coordinates; a reader to read first pixel data generated by first pixels of the image sensor at corresponding first times, the first pixels corresponding to respective sets of the pseudorandom coordinates; a comparator to compare the first pixel data with second pixel data generated by the first pixels at respective second times different from the first times to generate first change values; and a counter to generate a count of persons based on the first change values.