You can place a single image across two pages in BookWright using a page spread layout. There are several options for creating your page spread in BookWright and some best practices to follow. To remove a page spread first delete the image and then the image container.
Choose the page spread layout then drag and drop it to your pages.
Expand or draw an image container to cover two pages.
No matter how you create your page spreads don't place important content in the gutter where the two pages meet. And if you want your image to completely cover the page then make sure the edges of your image reach all the way to the page edge, (not just to the red dotted trim line).