I came up with this idea but I’m a little unsure about how to go about executing it.
It’s an A5 print booklet where the pages get shorter so that the image on the internal back cover is slowly revealed from the bottom up as the reader flicks through.
I’ve made a little (awkward) video which explains it a little better.
Interesting concept for the book, but the OP does not mention how the book would bind. If the book was wiro-bound or coil bound, this would be a simple task, and I would recommend using the page tool in indesign to set the pages at the correct sizes and positions. However, if this book was saddle stapled, this would be much harder (from a binding point of view).