I'll start off by quoting the winning submission.
Libraries have been trying to collect humanity’s knowledge almost since the invention of writing. In the digital age, it might actually be possible to create a comprehensive collection of all human writing that meets certain criteria. That’s what shadow libraries do - collect and share as many books as possible.
One shadow library, Anna’s Archive (which I will not link here directly due to copyright concerns), recently posed a question: How could we effectively visualize 100,000,000 books or more at once? There’s lots of data to view: Titles, authors, which countries the books come from, which publishers, how old they are, how many libraries hold them, whether they are available digitally, etc.
- https://phiresky.github.io/blog/2025/visualizing-all-books-i...
Basically, legally gray online book repositories such as Anna's Archive, who was the creator of this bounty, are trying to collect a lot of books. The question quickly arises - how many books are there?
The best way to track books is by using ISBN, international standard book number, basically the personal id of any given books, given to books by an international agency. Now that you know which books exist, you can check which books your repository already has and which ones are missing.
But ISBN covers the space of over 2 billion possible existing books. That's a lot. So, Anna's Archive has created a contest to display this space in the cleanest way possible. The winning submission is very nicely done, and in my view very well deserving of the 6,000$ bounty.