$(document).ready(function() {
var bgImage = $('#background-image');		
 
function resizeImg() {
      var imgwidth = bgImage.width(),
		   imgheight = bgImage.height(),
		   winwidth = $(window).width(),
		   winheight = $(window).height(),
		   widthratio = winwidth / imgwidth,
		   heightratio = winheight / imgheight,
		   widthdiff = heightratio * imgwidth,
		   heightdiff = widthratio * imgheight;
 
      if(heightdiff>winheight) {
        bgImage.css({
          width: winwidth+'px',
          height: heightdiff+'px'
        });
      } else {
        bgImage.css({
          width: widthdiff+'px',
          height: winheight+'px'
        });		
      }
	 
	 $("#background-image").show();
	  
    } 
    resizeImg();
    $(window).resize(function() {
      resizeImg();
    }); 



});

body{
    background: url(image.jpg) no-repeat center;
    background-size: cover;
}