Computer vision in classrooms [on hold]

I want to use computer vision to measure attention span of kids in a stereotypical class room. I plan to do it by measuring posture of kids and track their heads to see if they are paying attention. I plan to record classroom videos and then analyze so it need not be realtime. How should I go about implementing this ? Specific questions are

1) What are easy to use libraries ? (I assume OpenCV already in my list) 2) What all analysis should I do ? 3) are there any similar solution for crowd analysis ?

Any other input and help is much appreciated.