16. The system of claim 15 , further comprising: compare the second signature to a signature of a concept structure representing a pupil dilation to confirm a winding of pupil.
15. The system of claim 11 , wherein when determining using the first image and the second image if the viewer's pupil has been dilated the system is further configured to: generate a first signature for the first image; generate a second signature for the second image; compare the first signature to the second signature to determine if the first signature and second signature are substantially matched; and when the first signature and second signature are substantially matched, determine a pupil dilation.