onload = function () {
    setimages();
}

onresize = function () {
    setimages();
}

function setimages() {
    
    var currentwidth = document.body.offsetWidth;

    var imagewidth = currentwidth - 100;
    
    var imageheight = (400/1500) * imagewidth;
    var allimages = document.images;
    for( i = 0 ; i < allimages.length ; i++ ) {
        if((allimages[i].getAttribute("class") == "itemimage") || (allimages[i].getAttribute("className") == "itemimage")) {
            allimages[i].style.height = imageheight + "px";
            allimages[i].style.width = imagewidth + "px";
            if(imagewidth < 450) {
                allimages[i].src = "http://de-online.co.uk/images/mainimages/image.php?i=" + allimages[i].getAttribute("alt") + ".jpg&w=450";
            } else if(imagewidth < 800) {
                allimages[i].src = "http://de-online.co.uk/images/mainimages/image.php?i=" + allimages[i].getAttribute("alt") + ".jpg&w=800";
            } else if(imagewidth < 1200) {
                allimages[i].src = "http://de-online.co.uk/images/mainimages/image.php?i=" + allimages[i].getAttribute("alt") + ".jpg&w=1200";
            } else {
                allimages[i].src = "http://de-online.co.uk/images/mainimages/" + allimages[i].getAttribute("alt") + ".jpg";
            }
        }
    }
}