if (document.getElementById("divLandscape_Manage") != null) {
    var rnum = Math.random() * 1;
    picknum = Math.round(rnum);
    if (picknum == 1) {
        $("#divLandscape_Manage").css('background', 'url(images/landscapephoto/dallas_photo1.jpg) center top');
    }
    else {
        $("#divLandscape_Manage").css('background', 'url(images/landscapephoto/dallas_photo2.jpg) center top');
    }
}