Related articles about PNG and MNG compression

Here is an index of sites that host uncompressed, PNG-compressed, or otherwise-losslessly-compressed images which can be freely distributed, and can be used in compression tests.

• The Waterloo Image Repository ("BragZone")
  http://links.uwaterloo.ca/Repository.html
  The Waterloo Repertoire is a suite of 32 images (12 small grayscale, 12 medium grayscale, and 8 large full color), which includes the famous Lena.
• Kodak PhotoCD PCD0992
  http://r0k.us/graphics/kodak/
  PCD0992 was a set of 24 images in PhotoCD (N.B. not PictureCD) format, released by Kodak and put into public domain. The BASE resolution (768x512) was extracted and converted to RGB format. This set of RGB images eventually became a reference. Originally hosted by the Rensellaer Polytechnic Institute, the set is now available courtesy of Rich Franzen.