Hello! All the images I used to create the textures found here came from The Backyard Astronomer's Guide
by Terence Dickinson & Alan Dyers.
Technically the copyright for the original images would be to the photographer or whatever agency originally published them, and not necessarily to the book itself. I believe those credits are listed in the book, if I am not mistaken.
I do not claim, nor have I ever claimed, any rights to said images. I also don't put any rules on my textures for that very same reason. So long as they're not being used commercially, they're fair game for whatever people want to use them for. I'm not making any money off of them, and I don't think anyone else should, either. I just created them for fun, and if other people find them useful, great!
Having said all that, I appreciate your concerns about copyright! That's pretty important stuff. I'll try to get around to putting the name of the book in my descriptions soon in order to clear up any confusion.