Check the folder in which you must have imported the images, you can check that in the folder panel under the library module.
To save your book so that you can return to working on it after exiting the Book module, click the Create Saved Book button in the preview area.
In the Create Book dialog box, name the book, indicate if you want to save it inside a collection set, and choose other options. Then, click Create.
Thanks but the images are still located in the folder on my hard drive - they are just missing from the book and now from the collection I had previously created before i started the book. In the Collections panel in Library, my collection now only has 2 images and the book i created created shows zero pictures included. This is the problem I'm trying to solve.
Your method to save the book is exactly what I started doing but in the dialog box, I don't think I selected 'save it inside a collection' and that's when my problems began (e.g. the filmstrip only showing the 109 used photos and not the full 243 I wanted to use). Then, to make matters worse, in the process of trying to re-add the unused pictures back to the filmstrip, I think I somehow accidentally removed them from the collection and this might have caused them to then disappear from my book. The empty saved book shows up under Collections as a 'child' folder under its 'parent' collection.
Any other suggestions?