var clickmessage = "Right click disabled on images!"

function disableclick(e) {
    if (document.all) {//IE
        if (event.button == 2 || event.button == 3) {
            if (event.srcElement.tagName == "IMG") {
                alert(clickmessage);
                return false;
            }
        }
    }
    else if (document.layers) {
        if (e.which == 3) {
            alert(clickmessage);
            return false;
        }
    }
    else if (document.getElementById) {//chrome and mozilla
        if ((e.which == 3) && e.target.tagName == "IMG") {
            alert(clickmessage);
            e.preventDefault();
            return false;
        }
        if ((e.which == 1) && e.target.tagName == "IMG") {
            alert(clickmessage);
            e.preventDefault();
            return false;
        }
    }
}

function associateimages() {
    for (i = 0; i < document.images.length; i++)
        document.images[i].onmousedown = disableclick;
}

if (document.all)
    document.onmousedown = disableclick
else if (document.getElementById) {
    document.onmouseup = disableclick
}
else if (document.layers)
    associateimages()