wide background css3

This option isn't compatible with old navigator.

background:#color url(your url) no-repeat bottom fixed;

-webkit-background-size: cover; /* Chrome Safari */
-moz-background-size: cover; /* Firefox */
-o-background-size: cover; /* Opera */
background-size: cover; /* standard */

you only have to find a good compromise for the compression of your pics
For a compatibility for old navigator looks javascript.