I have the exact same problem. I have been speculating that it is the knowledge we are getting our picture taken which causes us to appear unnatural. My mother is very photogenic and looks great in pictures, but unfortunately I haven't inherited that from her. She is very easygoing and carefree about life in general and perhaps that is why she can appear natural in photos. What's even stranger is that we appear fine in the mirror. I have taken pictures of myself looking at myself in the mirror by holding my camera towards me while looking at a mirror at the same time so that I can see the camera's view in the mirror too, resulting in decent pictures. We just have to take it easy, and reduce stress when posing for the camera, act natural and not smile too broadly or whatever is causing us not to appear photogenic. I still haven't found a solution which works every time, but when posing for the camera, I try not to look directly at the camera, and a little bit off to the side so that I can forget that I am posing and act natural. Hope this works for you!