When you select a photo on a page in a book, the photo tool bar appears and the border of the photo is highlighted. There are two basic edit modes: move and crop. Below (see image) you're in the move mode. You can click and hold the mouse anywhere on the photo to move it around the page. Note that you cannot move it across to the other visible page.
If you grab one of the corner markers you can resize the photo. If you grab one of the diamond shapes at mid-points on each side, you can resize the photo frame and crop the photo. You can rotate the photo from the circular icon in the bottom.
If you select the icon that shows four arrows, the selected photo becomes the page background and completely fills the page (below). The single page background icon is highlighted in blue. You can zoom, pane and crop the photo in within its frame.
If you select the icon that shows four arrows on a two page spread, the photo fills both two pages (below). The same photo is spread across both pages. You can pane, zoom and crop the photos within the frame. Note that the two page spread icon is highlighted in blue.
You can remove the photo from a page using the trash can icon on the photo tool. This only removes the photo from that page. The same photo may still be in other pages and it is still in the project. See for more information.
There are also functions to order objects on a page (paper stack icons). If you have multiple overlapping objects (e.g. photos, text, embellishments) these functions let you bring the selected item to the top or move it to the bottom. Naturally these are only active if more than one photo or object is on the page. Below they're inactive because there's only one photo on the page.
If you switch edit mode to crop, the first icon in the tool bar changes as follows. The slider allows you to zoom in, pane and crop the photo.