Is your image in your header or footer or is it in the body of the document? Is it one image on one page or is it on all pages?

Note, you can have a full-page image as part of a header or footer.

The header and footer are in the bottom layer of the document, I believe. Text (and images) in the body will be on top of this.

If your image is on one page, not in a header or footer, the header and footer will not show up on top of it, the image is on top.

You can insert a text box (or two) and reproduce the text in your header/footer in the text box, which can be on top of the image. The text box is treated as a graphic by Word and can be on top of the image. The text box does not have to have any background (transparent) or border.

A page field can be inserted with the keyboard shortcut Alt-Shift-P.