The pictures used were released under a Creative Commons license that allows commercial reuse and modifications.
They are from:

naiad - a drawing by Farrah Sydney-Smith

thunderbirds - www.flickr.com/photos/jonbro/484718731/

forest - s0.geograph.org.uk/photos/91/68/916859_bae6b235.jpg

sunset - opencage.info/pics.e/large_967.asp

sam - www.woan.org/albums/2006GrandSlam/MG_6886.jpg

