1. A system for tracking one or more entities comprising: an image capture device for capturing image data describing an entity; a region generation module for generating a plurality of discrete regions, each region including one or more positions and describing a probability distribution over all positions in a region for one or more entities of interest; and an observation module coupled to the image capture device and the region generation module configured to, for each region: generate a set of particles for the region, each particle associated with an entity within the region; determine a weight associated with each particle, the weight describing a likelihood of observing the entity associated with the particle in the region; and modify the probability distribution associated with the region responsive to the weight associated with each generated particle.