PUZZLE 046 Baffling Bookcase

There's a photograph of a strange bookcase, where up and down don't seem to make sense.
To arrange the books as in the picture, what is the minimum number that would need to be glued to the bookcase to keep them in position?
You can't squash books into place by jamming them up close together, by the way.

Hint 1

The orientation of the photo and the orientation of the bookcase may not be the same.
Think about how the bookcase might be positioned.

Hint 2

Which way is down?
This will affect which books need to be fixed in place.

Hint 3

There's carpet around the bookcase in the photograph.

Super Hint

The photograph is taken from above a bookcase that is lying down on the floor.

Answer for 'Baffling Bookcase'

The answer is '0'.