Unless otherwise noted, the *.gz files were generated by the gzip command line tool and the .flate and .zlib versions were then generated by script/extract-flate-offsets.go. Similarly, the *.giflzw files were generated by script/extract-giflzw.go and the *.palette and *.indexes files were generated by script/extract-palette-indexes.go

The .jpeg files are usually the canonical versions of the testdata images, and other versions (.bmp, *.gif, *.png, *.tiff) were generated by ImageMagick's convert command line tool. The *.webp versions were generated by the cwebp command line tool.

256.bytes just holds “\x00\x01\x02\x03...\xff”.

bricks-* are various encodings of an original photo by Nigel Tao nigeltao@golang.org.

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.

hat.* are various encodings of a photo of “Self-Portrait with a Straw Hat (obverse: The Potato Peeler)” by Vincent van Gogh, held by the Metropolitan Museum of art. http://www.metmuseum.org/art/collection/search/436532 lists that image as in the public domain.

hibiscus.* are various encodings of a photo of “Hibiscus and Parrots” by Louis Comfort Tiffany, held by the Metropolitan Museum of Art. http://www.metmuseum.org/art/collection/search/13503 lists that image as in the public domain.

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.”

midsummer.txt is an excerpt of Shakespeare‘s "A Midsummer Night’s Dream", copied from http://shakespeare.mit.edu/midsummer/midsummer.1.1.html

pi.txt contains the digits of pi.

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

romeo.txt is an excerpt of Shakespeare's “Romeo and Juliet”, copied from http://shakespeare.mit.edu/romeo_juliet/romeo_juliet.2.2.html