Pls help with overlaying image over pinned elements/header

So im trying to keep a menu fixed at the top of the page, but I want an image (smaller than the width of the page) to overlay on top of the menu as It scrolls down. Ive tried pinning the menu to the top of the page and also placing the menu in the header, and then placing the image on a strip arranged to the front, but neither have been succesful. Any Ideas?
Thanks in advance!