You can have only ONE background image.I usually use the CSB PAGE PROPERTIES, Browse to the image and load it in.
If you want a background image in your TABLE so that it appears to have a layered look, it must be done manually.
Please view this page for samples AND instructions. EASY.
Bottom image (furthest behind) is put into the CSB page properties (or using code when necessary)
2nd layer (laying on TOP of the background image) is made by defining a table with an image background.
Then you can turn on/off borders of the tables and turn on/off cell colors of the tables to create the look you want.
KNOWN LIMITATION of the trick demonstrated on the page linked above:
Can not put a background image into a table that is INSIDE A TABLE without
hand coding the full table as seen in this page.