This shouldn't be difficult. The mirror shows exactly what you look like as you stand in front of it, except reflected across the plane of the mirror. It simply reflects light back to you so that you can see it. On the other hand, a photograph shows what was seen by the camera, and the effects of poor lighting and other such circumstances will be exacerbated by even the best of cameras - also, the resolution of commercial cameras is far less than that of the eye, so it can't capture all the detail of your appearance.
