When using a plane mirror, the image appears upright, at a distance in back of the mirror which is equal to the object (usually you, the person) in front of the mirror. Our eyes don't see objects, our eyes receive the incoming light that is reflected off those objects. A good way to test this is to stand in front of a plane mirror mounted on a wall, and turn off all the lights. You won't be able to see anything (in a totally dark room), much less a reflection in the plane mirror. Since our eyes collect incoming light, which is reflected off the silver backing of the mirror, our brains interpret the incoming image as a real image, although it is a virtual image, a false one, which looks like it is in back of the mirror. So if you move further away from the mirror, the reflected image in the mirror will also seem to move further away. If you move closer, the reflected image will also appear to move closer.
The distance of the imaginary image formed in the plain mirror (looking glass) is always equal to the distance of the person from the mirror. Therefore the distance of the person from his image is always twice the distance of the person from the mirror.
If the person moves away from the mirror by certain distance then the image will also move further away from the mirror by the same distance.
Please note that it is true only for the plain mirror.
The rules for the formation of image in concave or convex mirrors are altogether different. A convex mirror produces only imaginary image of a smaller size. A concave mirror can also produce real image with the size of image depending on the position of the object from the mirror.