When I released the rules for D6Pool under a Creative Commons license, I could not do the same thing for the illustrations because I hadn't licensed them that way from the artist. This creates the weird situation where the text is "CC By", but the images are all rights reserved.
For follow on books, I'm trying to derive all of the illustrations from public domain photography or artwork. I had a hard time at first, but I came across . I found a lot of what I needed there, and I've uploaded a dozen or so of my own photos as partial payback.
Does anyone know of other, better sites, or is anyone aware of issues I should know about with this site? I'd appreciate any advice.