function loginimg() {

    var v = document.getElementById("ctl00_ContentPlaceHolder1_newlogin1_DropDownList2").value;
    if (v == 3) {
        document.getElementById("ctl00_ContentPlaceHolder1_newlogin1_ImageButton1").src = 'images/fxz.gif';
        document.getElementById("zhmm").style.display = 'none';
    }
    else {
        document.getElementById("ctl00_ContentPlaceHolder1_newlogin1_ImageButton1").src = 'images/tu_12.gif';
        document.getElementById("zhmm").style.display = 'block';
    }
}