Media Query for targeting device ratio and DPI.

device-dpi.css

.box {
	    background: url( 'img/box-bg.png' ) no-repeat top left;
	    width: 200px;
	    height: 200px;
	}
	@media only screen and ( -webkit-min-device-pixel-ratio: 1.3 ),
	       only screen and (    min--moz-device-pixel-ratio: 1.3 ),
	       only screen and (      -o-min-device-pixel-ratio: 2.6/2 ), /* returns 1.3, see Dev.Opera */
	       only screen and (         min-device-pixel-ratio: 1.3 ),
	       only screen and ( min-resolution: 124.8dpi ),
	       only screen and ( min-resolution: 1.3dppx ) {
	
	       .box {
	           background: url( 'img/box-bg@2x.png' ) no-repeat top left / 200px 200px;
	       }
	
	}