This is a very common gesture cluster consistent with sadness. In this photo, Gerald Bingham, father of Mark Bingham, who perished on flight 93 on Sept. 11, 2001, shows a wrinkling of the muscles in the center of his forehead, while the outer (lateral) portions of his forehead is wrinkle-fee. This is the take home point in this photo - for in this context, it is a very distinctive and universal expression of grief.
Additionally, Mr. Bingham's eyes are closed, his head (neck) is down-turned and his mouth is covered. These four signs, when exhibited together, are a common gesture cluster of Sadness. This photograph was taken at a memorial service for the passengers and crew of flight 93, so we all know the context, and given this knowledge - it's easy to interpret. In our day-to-day lives, this cluster - and thus the emotion, is often missed in an acquaintance, co-worker, friend or even family member. When we lack context and insight into another's heart and mind, we need to be much more observant and reflective - and this is one of many situations where understanding nonverbal communication is wonderfully beneficial.________________________________________________________________________________________