A point object P emits rays of light to a plane mirror and be reflected to human eyes. Extending the reflected rays backward, we find that they meet at a point P' behind the mirror. Since P' is not real, it's a virtual image. The distance from the object to the mirror is equal to the distance from the image, do = di . The image is the same size as the object. Also, the image is upright if the object is upright but the right side will change to the left side.