var buffer = new Image();
var downloadStart;
var intervall = 8000; // = 8 Sekunden
var img = "http://vistar-capture.web.cern.ch/vistar-capture/lhc1.png?0.9253204172904482";

buffer.onload = function () { loaded(); };
buffer.onerror = function () { error(); };
document.getElementById('testa').src = img;
reload();

function reload() {
 downloadStart = new Date().getTime();
 buffer.src = img + "?" + downloadStart;
}

function loaded() {
 document.getElementById('testa').src = buffer.src;
 setTimeout("reload()",intervall);
}

function error() {
 setTimeout("reload()",intervall);
}
window.onload = reload;