The lighting setting can change a person's looks a great deal depending on how the light falls on the face and body. Because mirrors are present in different places, they can result in totally different images because of the difference in lighting settings.
There are two major different types of mirrors. Mirrors with the metal on the front and Mirrors with the metal on the back. Both Mirrors can give different images since they reflect light in different ways. See why do i look bad in photos.
The different components used in the mirror can either result in less or more refractive bending of the light and so in a different image. If the mirror's glass is replaced by plastic or if the glass is thinner, a different image might show up as a result.
The quality of the front and back surface of the glass can make a big difference in the image seen in the mirror. Low quality surfaces might distort or blur the image. See why i look ugly in videos.
If the mirror's glass doesn't have coating to reduce the reflection on the front face, the resulting image might be different, and in some cases a double image might show up.
Old mirrors might reflect different images as a result of wear in the glass surface or the metallic part. See why do I look ugly in some mirrors.
The mirrors used in some clothing stores might be designed to make a person look good. If the mirrors are more flattering, the person is more likely to buy clothes from the shop.
The surroundings can change the way the light is reflected, and so result in a different image. The color of the walls, curtains and the way light falls on them can result in different images.
If the mirror contains less iron, the image might look better. The iron in the mirror can give a faint greenish tinge to the skin. See why do we look ugly when we wake up.
The size of the room that has the mirror can result in different images because of the way the light is reflected. A small room could give a different image than a large room even if the same mirror was used.
The size of the mirror can result in a very different look. Car mirrors, for example, usually make people look different.
Most mirrors bend over time. The bending can result in a change in the way the light is reflected, and so the resulting image might be very different. See why do I look ugly in sunlight.