We can understand a mirror image using a ray diagram.
The image in the following simulation shows several light rays,
1, that originated by diffuse reflection at the person's nose. They bounce off the mirror, producing new rays,
2. To anyone whose eye is in the right position to get one of these rays, they appear to have come from a behind the mirror,
3, where they would have originated from a single point. This point is where the tip of the image-person's nose appears to be.
A similar analysis applies to every other point on the person's face, so it looks as though there was an entire face behind the mirror. The customary way of describing the situation
requires some explanation:
* Customary description in physics: There is an image of the face behind the mirror.
* Translation: The pattern of rays coming from the mirror is exactly the same as it would be if there was a face behind the mirror. Nothing is really behind the mirror.
This is referred to as a virtual image, because the rays do not actually cross at the point behind the mirror. They only appear to have originated there.