1. A pupil tracking system for automatically determining pupil responses, as recorded in a time-wise sequence of digital images of at least one of the subject's eyes, comprising: digital image processing means for identifying a location of a pupil of at least one of said subject's eyes in a plurality of said digital images in said sequence of digital images, comprising: center point determining means for identifying a darkest spot in the pupil of said eye, pupil geometry determining means for ensuring said pupil satisfies a minimum shape configuration, comprising: region-growing means for applying a region-growing procedure to said identified darkest spot of said pupil to expand the boundaries of said pupil to include regions of equivalent decreasing darkness; and pupil size means for computing a size of said pupil in said plurality of said digital images in said sequence of digital images.