I worked on early iris recognition software and we had already worked through this scenario way back then. If the scanner was worth it's salt, it would be doing what we did years ago...
1) Verify that the eye reacts to changing light conditions... Pupils should contract or dilate when required.
2) Verify that the eye isn't flat (i.e. a picture). Proper specularity orientation from changing light sources (we used infrared) to identify the curvature.
3) Glowing pupil under infrared, dark with different lighting.
I'm sure there were a number of other things we did, but it has been awhile. Bottom line is that we only used a representative frame from a video sequence for the iris coding; we used the sequence to verify that what we had was not a picture, a contact lens imprinted with an iris pattern, even a live person (not a corpse).
When I left that project, we were able to do iris recognition at a significant distance even if the subject was walking fast using high speed, high resolution video capture.