var elms = document.getElementsByTagName('a');

for (var i = 0, length = elms.length; i < length; i++) {
  (function (elm) {
    var overElms = [];
    var elmImgs = elm.getElementsByTagName('img');
    for (var i = 0, length = elmImgs.length; i < length; i++) {
      var elmImg = elmImgs[i];
      var overSrc = (elmImg.getAttribute) ? elmImg.getAttribute('overSrc') : elmImg['overSrc'];
      if (overSrc) {
        elmImg.setAttribute ? elmImg.setAttribute('outSrc', elmImg.src) : elmImg['outSrc'] = elmImg.src;
        overElms.push(elmImg);
        
        var elmCache = document.createElement('img');
        with (elmCache.style) {
          position = 'absolute';
          top = '0px';
          visibility = 'hidden';
        }
        elmCache.src = overSrc;
        document.body.appendChild(elmCache);
      }
    }
    if (overElms.length == 0) { return; }
    
    elm.onmouseover = function (event) {
      for (var i = 0, length = overElms.length; i < length; i++) {
        var elmImg = overElms[i];
        elmImg.src = (elmImg.getAttribute) ? elmImg.getAttribute('overSrc') : elmImg['overSrc'];
      }
    };
  
    elm.onmouseout = function (event) {
      for (var i = 0, length = overElms.length; i < length; i++) {
        var elmImg = overElms[i];
        elmImg.src = (elmImg.getAttribute) ? elmImg.getAttribute('outSrc') : elmImg['outSrc'];
      }
    };
  })(elms[i]);
}