jQuery(document).ready(function($) {
 
 var img;
$("#nav li").hover(
    function() { 
        img = $("<img src='/wp-content/themes/appleton/images/checkmark.png' width='28' height='29' class='check' />").prependTo(this); 
    },
    function() { 
        img.remove();
    }
);

if ($("#nav li").hasClass("current_page_item")) {
   
        $("#nav li.current_page_item").prepend("<img src='/wp-content/themes/appleton/images/checkmark.png' width='28' height='29' class='check' />"); 

 }
});