Heh, I never doubted the authenticity for a sec. This pic was actually taken by a professional photographer.
http://blog.alexbrownphotography.com/search/label/Sad Vader
Anyways, I always thought it was cute, sometimes inducing a melancholic state from years past. The ultimate highs and lows when your a child. I can imagine just a few minutes earlier he was having the time of his life watching Star Wars in the theater, only to be crushed because his parents didnt want to spend money on a Happy Meal. Or his father bought him the Vader outfit and took him out for a good time, before telling him he was divorcing his mother. Maybe he has worn the Darth Vader outfit for 3 days straight, simply refusing to take it off because he loves it so much.