var iValue, rNumber;
var img1 = new Image();
var img2 = new Image();
var img3 = new Image();
img1 = "http://www.taro-k.jp/img/eyecatch/1.jpg";
img2 = "http://www.taro-k.jp/img/eyecatch/2.jpg";
img3 = "http://www.taro-k.jp/img/eyecatch/3.jpg";

function display_image(){
iValue = Math.random() * 3;
rNumber = Math.ceil(iValue);
if(rNumber==0) rNumber++;
document.image1.src=eval("img" + rNumber);
}