bricks-* are various encodings of an original photo by Nigel Tao nigeltao@golang.org. The *.giflzw files were generated by script/extract-giflzw.go and the *.palette and *.indexes files were generated by script/extract-palette-indexes.go

harvesters.* are various encodings of a photo of “The Harvesters” by Pieter Bruegel the Elder, held by the Metropolitan Museum of Art. http://www.metmuseum.org/art/collection/search/435809 lists that image as in the public domain, and http://www.metmuseum.org/about-the-met/policies-and-documents/image-resources says that “You are welcome to use images of artworks in The Met collection that the Museum believes to be in the public domain, or those to which the Museum waives any copyright it might have, for any purpose, including commercial and noncommercial use, free of charge and without requiring permission from the Museum.”

pjw-thumbnail.* are various encodings of an image derived from an iconic, original photo of Peter J. Weinberger by Rob Pike r@golang.org.