The images on this page are all SVG files. SVGMagic normally only replaces these images if your browser doesn't support SVG, but on this demo page they will always be replaced thanks to the forceReplacements mode.
If you use the buttons above you will see that the image on the left has been replaced by a PNG image. The image on the right is the original vector image (assuming you are now using a browser that does support SVG images).
Sroll down for more demos.
SVGMagic also supports CSS background images. Just parse in the element and the option handleBackgroundImages and the script will do the rest!