If you want an image to completely cover a page in your book project you're looking for a full bleed layout.
What is a full bleed layout?
A full bleed layout extends to the edges of the page (or cover) so that the image or background color entirely covers the page with no uncovered edges or white stripes at the edges.
How to create a full bleed layout
When designing your book make sure your design reaches all the way to the page edge. Specific instructions for how to do this in each book-making tool are below. Also see our bleed examples.