Box Edges - Expanded!

Looking at the piles of boxes, you will notice one tricky thing.

The edges of the boxes seem to be expanded outwards.

Is this drawn on purpose? Or is our eyes playing tricks?

A frank message:
I did not modify the rectangular boxes.
The piling up of the boxes are, however, done on purpose to create the visual impression.

As such, it can be seen that our eyes do really play visual tricks on us.

Should we trust them...... What we see is not what we get!

:-)