Hopefully you've already "Saved" your book which creates a special collection including the photos and book template and details.
Then, to start on a new project, with your new photos selected, you can choose "Clear Book" - this will start over from scratch and you can build a new book from there.
The "Clear Book" button is right next to the "Create Saved Book" button:
Did all of the above (save book....clear book etc). This is not the first time i'm going onto a new book. I've done this many times in the past BUT this is the first time that previous book photos "hang" around in the Book module. something must have changed in a recent update.
I do experience something similar. Whenever I add a layout to a page one of the photo boxes is filled with a photo of the previous book I made. The photo is added at that moment also to the book collection.
This bug is recently introduced, I cannot be completely sure, but I guess it is introduced in 7.1 or 7.2.
While experimenting a bit further, first I noticed it does not happen always. Thereafter, I got (for every layout assignment):
Hello, I know this is not the answer you want to hear but this is a workaround.
As suggested click the button 'clear book'. Then click 'auto layout'. New images but unfortunately and old images will be added in the new book.
now click again clear book and again auto layout. Hopefully your problem will be solved.