If you have multiple pages and you want the same image behind the text on each page, you're in luck. When you copy the picture, the settings go with it. This means you only need to copy the initial image once after selecting the Behind text option. Click on the image on the first page and use the Control + C or Command + C keyboard shortcut to copy the picture to your clipboard. Then, go to the next page and use the Control + V or Command + V shortcut to paste the image.