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, brick001.jpg and metal003.gif were downloaded from
http://www.grsites.com/archive/textures/
a collection of free background images.
brick-height-map.jpg is derived from brick001.jpg.
metal-height-map.jpg is derived from metal003.gif.

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

Puffer is from an example on the Widipedia page
https://en.wikipedia.org/wiki/Conway%27s_Game_of_Life

I made the other images. (David Eck, eck@hws.edu)