You can change the layer of your placed Items,
and you can move them forward or backward.
How To:
Open the「Placed Item List」on the left side of the screen,
And long press on an Item in the list.
If the Item display shifts to the left,
you will be able to move the Item up or down.
If you long press on an Item and move it up or down,
the Item layer will change either forward or backward.
If you remove your finger in the place where you want to move it, it will appear in the background of Items where the layer is higher.
In the Item list, the Items at the top are in the foreground,
the Items at the bottom are in the background.
The background image itself is fixed,
and cannot be moved forward or back.