var imgList = new Array(
						"../img/top_pic1.jpg",
						"../img/top_pic2.jpg",
						"../img/top_pic3.jpg",
						"../img/top_pic4.jpg"
						);
var rnum = Math.floor(Math.random()*100) % imgList.length;
var output = "<img src="+imgList[rnum]+">";
document.write(output);