Does anyone have any thoughts on how I can add more detail to the hair in this picture. I am working on transforming it into a Andy Warhol style portrait but the hair as no detail or depth. I thought rendering it would help but it really needs something else.

I would maybe take r find another photo that is close to the same pose for each person, then cut and paste the hair texture in...it should work ok for what you want to do.

I think the faces are also blurry and the photo very poor overal so that if you did add hair with detail it would look out of place with the rest of the blurred image.