var oImgs=new Array( "images/f1.png", "images/f2.png"); 
for(var k=0;k<oImgs.length;k++){(new Image()).src=oImgs[k];}
function randomImg(){

		var n=oImgs.length; 
		
		var currIndex=parseInt((Math.random() * n),10);
		document.getElementById("thebd_t1").style.backgroundImage="url("+oImgs[currIndex]+")";
		if(currIndex==0){
			var subdiv = document.getElementById("thebd_t1_sub_div");
			document.getElementById("thebd_t1").appendChild(subdiv);
			subdiv.style.display='';
		}
		else {
			document.getElementById("thebd_t1").innerHTML='';
		}
}