Internet Explorer < version 9 background resize less mixin. An easy way to get css background-size: cover in internet explorer versions 8 and lower. Add it to your mixins less file and reference wherever you need it.

IE7-8 Background Resize Mixin

// used to make a background image (including alpha images) scale to the size of it's container in ie7 & ie8
.ie7-8-backgroundScale(@filename) {
    filter:progid:DXImageTransform.Microsoft.AlphaImageLoader(src='@{filename}', sizingMethod='scale');
    -ms-filter: "progid:DXImageTransform.Microsoft.AlphaImageLoader(src='@{filename}', sizingMethod='scale')";
}