Comparing the lighting conditions as well as comparing what is more accurate mirror or camera. Different lights in the bathroom, window lights and overhead lights cast different shadow on the face, making you look different in each environment. You can also try changing the exposure and contrast settings automatically with a camera, and compare your reflection and photos under the same natural, soft lighting, Visuals Clipping recommends. Both of these points are not true in all cases, but when consistently lit, you can judge details of the face and color of the skin fairly.