function searchbox_click() {
    document.getElementById('searchbox').style.backgroundImage = '';
}

function searchbox_onblur() {
    var str_searchbox = document.getElementById('searchbox').value;
    if (str_searchbox.length < 1) {
        document.getElementById('searchbox').style.backgroundImage = 'url(/images/searchbox-google.jpg)';
    }
}