Why Can't Observer See Image 4 & 3 in 2 Plane Mirrors?

[kenny1999]

there is two plane mirror which is placed perpendicular to each other, as shown in the figure below. An object (indicated by the red dot) is placed
in front of the mirrors and then there are 5 image formed (indicated by the blue dot 1,2,3,4,5, as illustrated in the figure)

which image that the observer CANNOT see? I know the answer is image 4 and 3, but why? I want to know why the observer cannot see image 3,4
and why he can see image 1,2,5... Thanks all

 

[rl.bhat]

The position of the object is such that any light from the object cannot go through point 3 and 4, because they are in the plane of the reflection of mirror1 in mirrpr2 . Draw the ray diagram and verify your self.