function rollover() {
    var images = document.getElementsByTagName("img");
    var imgLength = images.length;
    for (var i = 0; i < imgLength; i++) {
        images[i].onmouseover = mouseOver;
        images[i].onmouseout = mouseOut;
    }
}
function mouseOver() {
    this.src = "box2.png";
}

function mouseOut() {
    this.src = "box1.png";
}
