Ugh. I hate it too. I always seem to have some glaring imperfection and I think I look hideous/stupid/gross/strange.
Everyone looks better smiling though. Seriously. Happiness is pretty. If you look like "Oh God, get away from me! I look awful and I hate having my picture taken!" you're probably not going to look very good in the picture.
Some people are just more photogenic than others. Lucky ducks. But beauty is not just skin deep and cannot always be captured by a camera.