Device pixels (resolution) or viewport pixels (like in CSS)? I mean OS manufacturers could just change the way viewport pixels are calculated in their viewport rendering, which makes the law redundant. And relying on device resolution doesn't make any sense for modern devices with hidpi displays.
I'm guessing they are only thinking of raster images, like excerpts of photos or videos.
Someone somewhere will come up with a JPG to SVG or CSS converter for images, if it doesn't already exist.