Besides a full text version of the book, that mini-site also contains some simple illustrations made by the author. Looking at the bottom of the “Outer” image, I saw the following copyright notice: “Vernor Vinge, 2006 (Using the GIMP)”
This is not entirely surprising, considering that he is a friend of Free Software and even a member of the award committee for the FSF Award for the Advancement of Free Software. But still, it is nice to see a well-known SF author who is also a GIMP user. As a GIMP developer and SF fan, this made me happy.
I doubt that Vernor Vinge will ever read this blog, but for the next illustrations I would recommend using Inkscape for the line art and text. This would lead to better results than using GIMP alone.