The W3C CSS Background and Borders Module Level 3 (currently a working draft) defines the background-size property that fits our requirements.
I think all developers are baffled at why Internet Explorer still fails to support this very popular (albeit troublesome) property. It’s been around so long, that we often forget that it’s actually a CSS3 property. Although IE doesn’t offer support for the opacity property, it does offer similar transparency settings via the proprietary filter property: