1. A method for determining one or more characteristics of a subpopulation of objects from images collected from a population of objects, comprising the steps of: (a) imaging the population of objects to collect image data, while there is relative movement between the population of objects and an imaging system used to image the population of objects; (b) using the image data to define the subpopulation of objects, the subpopulation of objects being encompassed by the population of objects; (c) identifying an object feature exhibited by the subpopulation of objects; and (d) using the image data to measure at least one characteristic associated with the object feature.