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