When the image of an object is seen in a plane mirror, the distance from the mirror to the image depends on the distance from the object to the mirror.
It is because a Plane Mirror is the incident ray, the reflected ray, and the normal to the surface all lie in the same plane, and the angle of incidence is equal to the angle of reflection. So, the distance from the object to the mirror equals the distance from the image to the mirror. Thus whoever the person viewing this image must sight at this image location.
