i think you pup is unsure of what you are doing and then not sure if they are in trouble or not when they are told to stay..try for some action shots..or taking a pic when they don't know you are doing this..keep the camera around so it is familiar..tape a favorite little toy to the top..or try holding it in one hand while you do sit and stay..then reward with a treat. Do it for a few days in a row then try to take your pics and i think you will see more of a smily face thru the lens.
Shadow,
My dog Bear is afraid of the camera, so his pics never come out that good either. He doesn't look sad though, just scared. I liked Smkie's tips, I'm going to try that myself. BTW, looking sad or not, your dog is adorable.
yes I find that holding up teddy's tennis ball gets a reaction from him he perks his ears up (as much as he can lol) and you can see it in his eyes that he wants that ball lol he's got that "throw the ball throw the ball throw the ball throw the ball" look in his eyes hahaha