The camera really does add (the appearance of extra) weight, and it's not always only 10 lbs. (The bigger you are, the more weight it adds). Everyone looks wider in a photograph then in real life. The effect is so subtle, that we don't recognize it easily in other people, just in ourselves (just as we notice when we've put on a little weight, but don't see other people's weight gain until it's pretty obvious).
Because the photograph is two dimensional, and you're three dimensional, the photo is somewhat a "flattened" image of you, and therefore wider.
Use the tips photographers use, to get a more realistic image of you. Stand at a slight angle. Imagine a clock-face if the photographer is at 12 looking at 6. You are standing in the 6 o'clock position, but instead of facing 12, face somwhere around 10 to 11 o'clock.
Then elongate your neck, and cock your head slightly (if you've ever had a professional photo taken you know the position I'm trying to explain).
Candid "surprise" photos are rarely flattering, but if you have a few seconds to pose, you'll look more like your real-life self in photos.