var blnDOMSUPPORT = (document.getElementById) ? true : false;
function swapBrandingImage(){
   if ( blnDOMSUPPORT ){	
      var imgMain = document.getElementById('mainbrandingimage');
      var divParent;
      var imgNew = document.createElement('img');
	  imgNew.src = document.getElementById('swampimage').src;
      imgNew.id = 'mainbrandingimage';
      divParent = imgMain.parentNode;
      divParent.replaceChild(imgNew, imgMain);
   }else{
      document.images['mainbrandingimage'].src = document.images['swampimage'].src;
   }
}  
swapBrandingImage();