This will be used to read your mail without opening it, if anyone wasn't yet sure. It reads through 9 layers. If you read from both sides of an envelope, that's 18 layers. So, the envelope is 2, and 5 sheets trifolded makes 17 layers total. So letters with 5 or less pages can now be read and stored for big data and trial evidence. Pretty decent actually.
The work described is very interesting, although when I first read the headline I thought the article would be about training a model that predicted book ratings based on book cover images. That sounds like a fun experiment to try, too.