[ValerieUSA]

I think the sun is directly in front of the men and overhead, casting a shadow in the direction the head is leaning. Thus an under the chin shadow on one man, and side shadows on the men whose heads are turned and slightly tilted in opposite directions.
However, even with that explanation, it does look a little fishy... if my camera wasn't broken right now I would try to recreate such a scene around noon. Maybe someone else could give it a try.

[rusty millet]

The shadow for the center man in t-shirt is the same as Kerry. Following the hypothesis of a doctored photo, the man on left would have been inserted, not Kerry.

[Robert A Cook PE]

Look at my questions about the photograph being edited in Nbr 149.....

Not only do the shadows differ from Kerry's side of the photograph to the crew's side, but the transition in the middle has objected distorted and moving.

[RetSignman]

Look at the watch the guy with glasses, has on. Can you make out the time?