在页面加载iframe时显示图像

I have a website with a menu, when menu item is clicked I display the page for that menu in an iframe(iframe is set to display home page initially by default). sometimes it could take few seconds to display the page for the selected menu item (for example reports) and I would like to display a loading image while the page is loading. how to do this using javascript or jQuery (sample code will be helpful)? thanks in advance.I have a website with a menu, when menu item is