How to add an image across two pages/a spread

Full image:

For a full bleed image (from edge to edge of the page) add one image box that spans across the entire spread. From there you can drag and drop an image from the left margin into the image box(es).

 

Image with a border:

If you would like to have a border around the image, add an image box that is within the inner area of the blue safety line. From there you can drag and drop an image from the left margin in the photos tab into the image box(es). You can then add a background that is your desired color or pattern - or add an image shape the size of the entire page and select your preferred color.