To exclude photos from your book, simply do the following:
Tap on the Monthbook, Monthly Mini or Classic Chatbook that needs editing
Long-tap on any photo to bring up the option to select more than one photo
Tap "x" on each photo that you'd like to remove or select multiple photos from your book and then tap "Exclude" on the bottom left
Tap "Done Rearranging"
You can also tap on a single photo
Tap the 3 dots in the upper right hand corner
Tap "Exclude Page"
To view a step-by-step video on how to exclude photos from your Chatbooks (iOS):
Learn how to exclude/remove photos from the Chatbooks website here.