It does not appear that you can include an image on each page of the Ancestor Book or in the publishing center. You can try and go to Legacy's website to request a suggested enhancement to the program.
However, a way around this would be to take the necessary number of sheets to print your report (based on the print preview) and print the image in the desired place on the pages ahead of time. You would be creating your own 'stationary'. You would probably have to adjust your report headers in Legacy so that you do not print on top of the image, but I think it would work.
Good luck! Let us know how it turns out. I would be curious to know if it was successful.
Brian