Estoy usando validate jquery plugin y recaptcha para un formulario de contacto y me gustaría saber cómo puedo verificar si el código en el captcha es correcto antes de que se envíe el formulario si no se envía un mensaje de error porque ahora valido todo, pero inserté un código incorrecto el formulario se envía de todos modos. Aquí está mi código de antemano para cualquier ayuda

<script type="text/javascript">
             var RecaptchaOptions = {
                lang : 'en',
                theme : 'custom',
                custom_theme_widget: 'recaptcha_widget'
             };
            </script>

            <form id="contact" method="post" action="#">

                <fieldset>
                    <label for="name_contact">NAME</label>
                    <input type="text" class="input-xlarge" id="name_contact" name="name_contact" value="" placeholder="" minlength="2">

                    <label for="email_contact">EMAIL</label>
                    <input type="email" class="input-xlarge" id="email_contact" name="email_contact" value="" placeholder="">

                    <label for="telephone">CONTACT NUMBER</label>
                    <input type="tel" class="input-xlarge" id="telephone" name="telephone" placeholder="" value="" >

                    <label for="message">MESSAGE</label>
                    <textarea id="message" class="input-xlarge" name="message" placeholder="" rows="5"></textarea>                  

                    <div id="recaptcha_widget" style="display:none">

                        <div id="recaptcha_image"></div>
                        <div class="recaptcha_only_if_incorrect_sol" style="color:red">Incorrect please try again</div>

                        <span class="recaptcha_only_if_image">Enter the words above:</span>
                        <span class="recaptcha_only_if_audio">Enter the numbers you hear:</span>

                        <input type="text" id="recaptcha_response_field" name="recaptcha_response_field" />

                        <div><a href="javascript:Recaptcha.reload()">Get another CAPTCHA</a></div>
                        <div class="recaptcha_only_if_image"><a href="javascript:Recaptcha.switch_type('audio')">Get an audio CAPTCHA</a></div>
                        <div class="recaptcha_only_if_audio"><a href="javascript:Recaptcha.switch_type('image')">Get an image CAPTCHA</a></div>

                        <div><a href="javascript:Recaptcha.showhelp()">Help</a></div>

                    </div>

                    <script type="text/javascript"
                        src="http://www.google.com/recaptcha/api/challenge?k=6Lf8RN4SAAAAAKnllVnDw23UpBIuAIdTRFgN1kmX">
                    </script>

                    <noscript>
                        <iframe src="http://www.google.com/recaptcha/api/noscript?k=6Lf8RN4SAAAAAKnllVnDw23UpBIuAIdTRFgN1kmX" height="300" width="500" frameborder="0"></iframe><br>
                        <textarea name="recaptcha_challenge_field" rows="3" cols="40"></textarea>
                        <input type="hidden" name="recaptcha_response_field" value="manual_challenge">
                    </noscript>             

                    <button type="submit" value="" id="" name="send" class="pull-right lightblue btn-primary">SUBMIT</button>
                    </fieldset>
</form>


<script type="text/javascript">
    $(document).ready(function () {

        $("#contact").validate({
            rules: {
                "name_contact": {
                    required: true,
                    minlength: 3
                },
                "email_contact":{
                    required: true
                },
                "message":{
                    required:true
                },
                "recaptcha_response_field":{
                    required:true
                }

            },
            messages: {
                "name_contact": {
                    required: "Please, enter a name"
                },
                "email_contact":{
                    required: "Enter a valid email"
                },
                "message":{
                    required: "Please provide a comment"
                },
                "recaptcha_response_field":{
                    required: "Captcha is required"
                }
            },
            errorPlacement: function(error, element) {
                error.insertBefore(element);
            }
        });

    });
</script>