I came across this site and saw that it had a couple of blurry images. I checked my browser zoom in Firefox and Chrome and they were both 100%. I copied the images to look at them in Photoshop and Paint, and they were both sharp and displayed smaller.
My first thought was that it was browser zooming, but it's not. As far as I can tell, there's no CSS coding to make the images bigger in the browser. It's nice and sharp at 75% zoom in Chrome. What's that about? Screen Resolution?