A system includes a sensor and a tracking subsystem. The tracking subsystem receives an image feed of top-view images generated by the sensor. The tracking subsystem detects an event associated with an item being removed from a rack. The tracking subsystem determines that a first person and a second person may be associated with the event. In response, the tracking subsystem dilates contours associated with the first and second person from a first depth to a second depth until the contours enter a zone adjacent to the rack. A number of iterations is determined for each contour to enter the zone adjacent to the rack. If the first person's contour enters the zone in fewer iterations, the item is assigned to the first person.