var x=true;
function switchImage(imgSrc) 

{
imgName = 'panelControler'
  if (document.images)

  {

    if (imgSrc != "none")

    {

      document.images[imgName].src = imgSrc;

    }

  }

}

function toogleImage(){
x=!x;
if (!x) {switchImage('images/showPanel.gif'); }
else if (x)  {switchImage('images/hidePanel.gif'); }
}