Sendding image to front in HTML

Ok my problem is dat i have 2 images
I required for formatting & other for background

what i need is to send formatting image to back so that it may be hidden from viewers & bring the background image in front (so that it covers the
formatting image)

How to do this guyz
I need it for my blogger template
I think its XML (same as HTML I think )

or

Some one just tell me how to add a transparent image for formatting in blog