function changeImg(){
    document.getElementById('ctl00_imgSupport').src = (document.getElementById('ctl00_imgSupport').src.indexOf("btn-support.gif") == -1) ? "/imgs/fr/btn-support.gif" : "/imgs/fr/btn-support-on.gif";
}
window.onload = function(){
    var xTimer = window.setInterval("changeImg()",500);
}