To the best of my knowledge, they are public-domain and free for use in any way you choose.
Backgrounds
Bold & Bright
Backgrounds 2
Mostly Light
Backgrounds 3
On The Darkside
Backgrounds 4
Miscellaneous
Backgrounds 5
Splotchy, Blotchy & Blobby
Backgrounds 6
More Miscellaneous.
(Getting a little hard to categorize them all.)
Big Backs
Big Backs are all sized to 565 x 410 for use as "full cover" backs, aka "css backs" or "postcards".
Big Backs 2
Big Backs 3
Fractal Backs
