Abstract: A time-varying image of a circulating venue containing a flow of particles is generated by imaging using a video camera and a digital frame grabber. Spatio-temporal intensity gradients within each of the images are generated. Particles are then identified within the images. A particle is matched with a corresponding identical particle from other images using, for example, a heuristic equation that measures similarity of shape, size, and position. The distance of translation of the matched particle from one image to another is determined. Leukocyte velocity is determined by dividing the translation distance by the time differential between the images. The first five statistical moments of frequency distribution of the velocity may also be determined.