How to use CSS media query to scale background-image to viewing window

Question

For the background of a website, I have this sizable picture:

body {
    background: #000 url(/assets/img/living.jpg) no-repeat center center;
    background-attachment: fixed;
    -webkit-background-size: cover;
    -moz-background-size: cover;
    -o-background-size: cover;
    background-size: cover;
    height:100%;
}

However, the background-attachment: fixed setting doesn't seem to be having the same impact on my mobile device (iPhone 4S running Safari) as it would on a desktop. Can I use a media query to change it and why is that the case?

Answer 1

If you only want the desktop version of the image to be downloaded...

just the mobile image will be downloaded to the mobile device -

To establish a minimum browser width for the desktop image, you must use a min-width declaration...

as well as a maximum width for the mobile image