function switch_product_img(divName, totalImgs) {
        for (var i=1; i<=totalImgs; i++) {
        var showDivName = 'photo_' + i;
        var showObj = document.getElementById(showDivName);
        if (showDivName == divName)
                showObj.style.display = 'block';
        else
                showObj.style.display = 'none';
        }
}