var ka_imgl = new Image();
var ka_delay = 600000;
var ka_imgt;

function ka_random_img() {
	// once the image has loaded, perform an action
	ka_imgl.onload = function() {
//		alert('all ok?');
	}
	ka_imgl.src = '/spt/image.php?jsid=keep+alive&rand=' + Math.floor(Math.random() * 1000);
	setTimeout( 'ka_random_img()', ka_delay );
}
setTimeout( 'ka_random_img()', ka_delay );