Position of the (mirror)image

If you take a look at your image in the mirror, the image appears "behind" the mirror. The exact position of the image (the virtual image) can easily be determined with a glass plate.
In order to do that, you take a sheet of paper with any kind of drawing on the one side of the sheet. Place the glass plate in the centre of the sheet (see picture below).

The surface of the glass also creates a reflexion. If you take a look through the glass plate from the side of the drawing (see red arrow in the picture below), you can see the reflexion of the drawing on the empty side of the sheet of paper (see picture below). Now, take a pen and redraw the reflexion while looking through the glass.

Now you can easily measure the distance between the first drawing and the glass plate, as well as the distance between the glass plate and your own drawing. What can you say about that?