The best thing to do is mostly just disable images altogether.
Today's web is racing ahead with broadband connections in mind and it's a darn shame, if you ask me, that internet uptake in some parts of the world is so slow.
Of course, but the idea was that it wouldn't become blurry when zoomed, given enough resolution.And that doesn't even really address physical problems. Monitors are limited to 72ppi resolution anyway, no matter how big your screen is. Higher resolutions don't always make a visible difference.