Detectobject - track eye blink


i want to track eye blinks. my idea was to use detectobject to get the coordinates of the eyes, and then analyze these region of the videofeed with a pipet.

the only way i can realize this is by creating black quad with the tracking data, using the colour information to select the according pixels out of the pipet spread.

but that seems quite ugly to me. any ideas for a more skilfully solution? thx