While there are images created by a single reflection at each mirror, we are interested in the image created by two consecutive reflections at both mirrors. An observer at $A$ can see such image of point $B$ at $B''$, while an observer at $B$ can see such image of point $A$ at $A''$. (Needless to say, an observer can see an image when facing it.) Unlike the images created by a single reflection (such as those at $A'$ and $B'$, the image created by two consecutive reflections are not inverted (or doubly inverted). Note that the image of point $A$ at $A*$ is not observable by the observer at $B$, but may be observed from other positions.
