Earth-1024x512.jpg is a resized image from
http://maps.jpl.nasa.gov/ (courtesy NASA/JPL-Caltech)
Image can be freely distributed but should credit
the NASA/JPL-Caltec.

marble,jpg and brick001.jpg were downloaded from
http://www.grsites.com/archive/textures/
a collection of free background images (that
no longer exists).

Earth-512x256.jpg is a version of an image
that seems to be all over the Internet. I don't
know its original origin.

mona-lisa.jpg is from Wikimedia and is in the public domain
https://commons.wikimedia.org/wiki/File:Mona_Lisa_headcrop.jpg