1. cold state = native (probably white)
2. cursor over body element ('near image') = dim chequerboard (white/light grey)
3. body being clicked = contrasting chequerboard (white/black)
4. over image = solid light grey
5. image being clicked = solid black

Test
nice local res image: chrome://branding/content/about-logo.png
big press http://mozcom-cdn.mozilla.net/img/covehead/about/logo/download/logo-only.png

Update of http://freestyler.ws/style/3447/center-images-dynamic-background for Fx4. Fx4 changed the structure of image-only page, so the old one no longer works and Fx4 lacks some possibilities seen in Fx3.

Notes:
- this time without url-prefix restrictions, lets see what happens

Changelog:
2011-06-13 rebirth
2011-06-15 image-rendering: -moz-crisp-edges just for the image
2011-08-31 image-rendering: -moz-crisp-edges just for the image in 'non-cold' state. That is you'll see downscaled images untouched ('smoothed') as usual until you move your cursor over viewport. After that image gets old nearest-neighbour 'sharp' rendering, so after any kind of artificial zoom (eg. using http://www.mousegestures.org/ ) you'll see actual sharp pixels and not the blurry fog. Indeed, only as long as you stay within viewport.

For Chrome try http://freestyler.ws/style/77460/chrome-center-images-dynamic-background