Why and how does the author use visual pictures?

As I read this book, I asked myself the same question. 
The pictures seemed to sneak up on me, and were a bit unexpected and shocking.  My
answer or explanation for them is this:  it seems to me that the author is using them to
reiterate what is going on in the book at the time the pictures/art are inserted.  Oskar
is a bit disheveled, and therefore, the presence of the pictures don't make sense at
first, either.  Upon closer examination, you see the world through Oskar's eyes...a
young man who is confused, wandering, trying to make sense of a world which was one day
safe and full of the loving family to which he was so accustomed.  Suddenly, that world
changed into a dangerous place that can whisk away loved ones in a heartbeat without
explanation or warning.

In a way, too, these pictures
underscore the fantasy world that Oskar is viewing...a sort of magical realism...this is
especially true for the falling man sequence of pictures at the end of the book.  The
man does not fall downward as one would expect...the pages, when flipped, show him
falling upward.  Toward the safety of the building which hasn't yet collapsed, or toward
Heaven?  It is in the eyes of the young boy...we can only make suggestions as to what
Oskar is trying to do, explain, or carve out for himself and his mother in this new,
more ominous existence.  Oskar keeps imagining things in reverse, back to the time his
father was still alive and leaving messages on the voice mail machine.  I think that is
what these pictures and art are doing for us...showing us Oskar's inner self and
wishes...showing us the world as he wishes it were.