[DerekM]

You can insert images into the header/footer fields. Those are accessible under the Print panel. You may need to also modify the margins to accommodate the size of the image which are also done in the Print panel.

You can save a file as template that has this image added and make new documents off of that. You can not however using the style theming to apply this template and get the image. Theming only concerns things that are styles and header/footers are not considered styles.

If you have any questions about this, just let me know!