> If there was a Borgesian book containing, say, all possible 512x512 images, one on each page, then surely two people having the same copy of that book wouldn't need to exchange images, they could simply exchange page numbers, and see exactly what the other one is referring to.

If that were the case, the page number would be as long as the image, and exchanging one or the other is the same. Heck with proper order arrangement, the page number IS the image, in a known format.

In other words, the information content of such book is exactly 0.