More at https://www.c82.net/blog/making-of-naturalists-library, you can see that the source material was actually in pretty good condition, just aged and yellowed; they used Photoshop's AI to stitch drawings that were spread out over two pages together. And probably some upscaling.

AI was used to "fill in visual gaps"

> Not only did AI tools then help him unearth need­ed sources and fill in visu­al gaps

I think that's clear