function imgFix() {  
  //定義要限制的圖片寬高,這個寬高要同style裡面定義的相同，小於限定高寬的圖片不操作  
  var widthRestriction = 100;  
  var heightRestriction = 100;  
  var allElements = document.getElementsByTagName('*')    
  for (var i = 0; i < allElements.length; i++)  
  {  
    if (allElements[i].className.indexOf('imgBox') >= 0)  
        {  
      var imgElements = allElements[i].getElementsByTagName('img');  
      for (var j=0; j < imgElements.length; j++)  
          {  
        if ( imgElements[j].width > widthRestriction || imgElements[j].height > heightRestriction )  
                {  
          if ( imgElements[j].width > imgElements[j].height)  
                  {  
            imgElements[j].height = imgElements[j].height*(widthRestriction/imgElements[j].width);  
            imgElements[j].width = widthRestriction;  
          } else  
                  {  
            imgElements[j].width = imgElements[j].width*(heightRestriction/imgElements[j].height);  
            imgElements[j].height = heightRestriction;  
          }  
        }  
                if ( imgElements[j].height < heightRestriction )  
                {  
                  imgElements[j].style.paddingTop = ( heightRestriction -imgElements[j].height ) /2 + "px";  
                }  
      } /*for j*/  
    }  
  }/*for i*/
}  
 
window.onload = imgFix;