O'Reilly is a publisher, not an author (unless you mean a specific person). Start here:
http://www.oreilly.com/
If you don't have a specific book in mind, maybe you can visit B&N and find the specific one you saw, and proceed from there.
I'm responding to your request, "Do you have any ideas?", and just outlining ideas for ways to proceed on this. I'm not saying any particular idea will work out, or that you'll definitely end up with an answer. You asked for ideas, so I'm posting ideas.
Capturing screenshots is both widely used and widely known.
Capturing screenshots of Setup Assistant, however, is both uncommon and poses a unique set of restrictions. I say it's uncommon because a book is the only reason I can think of to make such screenshots. That alone makes it uncommon, as relatively few people here are book authors. It's also a unique set of restrictions because no user accounts exist yet (unless one is redoing the procedure).
Personally, I would start by finding a specific book with such screenshots, and asking the author. This falls under the engineering maxim "Don't reinvent the wheel". In other words, if someone has already solved the problem, a good starting point is to ask them how they did it. Unless it involves a proprietary tool or a trade secret, book authors are generally open to questions about how they do things.
If I was completely unable to find any actual book, or a forum for the book proved completely fruitless, I'd probably look into the 'Grab' utility (google search terms: mac os grab tool). Yes, this may well take some technical skills, and the ability to dig into the underpinnings of the OS while Setup Assistant is running. I have the skills to start that research, but I still can't predict how it would turn out. It could fail completely, and even if it worked out, it might turn out to be a fairly complex process. There's also no way of knowing how difficult the research itself would be. It could take hours and hours to figure out. That's a lot less appealing than finding a book and asking the author.
In short, the requirement that it work in Setup Assistant means this is a markedly more difficult problem to solve.