$(document).ready(function() {
    $("#search_form").validate({
        rules: {
            search_string: {
                required:true
            },
            captcha: {
                required: true,
                remote: "/public/captcha/includes/process.php"
            }
        },
        messages:{
            search_string: {
                required: "X"
            },            
            captcha: {
                required: "X",
                remote: "X Image Code"
            }
        }
    });

});