function ImgOnClick(img, tbid, id, clientid)
{
 
      var tb = document.getElementById(tbid);
      
      var src = img.src;
      
      if(src.indexOf("cbUnchecked.gif") > 0)
      {
        tb.value = tb.value + "," + id;
      }
      else
      {
        tb.value = tb.value + ",-" + id;
      }

      __doPostBack(clientid, '');
 
}

function DoLabelClick(id, tbid, clientid)
{
    var imageId = 'img' + String(id);
    var img = document.getElementById(imageId);
    ImgOnClick(img, tbid, id, clientid);     
}