background.jpg is based on https://www.gnu.org/graphics/meditate.xcf.gz
which can be found at https://www.gnu.org/graphics/meditate.html
Check that webpage for licensing information to see what conditions the image falls under.

gnulove.jpg based on the image found at https://www.gnu.org/graphics/gnulove.html

Look at those pages to see what copyright license they fall under.
