This is what is generated in html page:
<pre>
<div id="rc16">
<script type="text/javascript">
var RecaptchaOptions = {
theme : 'custom',
custom_theme_widget: 'recaptcha_widget'
};
</script>
<div style="display: none;" id="recaptcha_widget">
<table width="100%" class="captcha">
<tbody><tr>
<td colspan="2"><div id="recaptcha_image"></div></td>
</tr>
<tr>
<td colspan="2">
<label class="recaptcha_only_if_image captcha">Enter words above:</
label>
<label class="recaptcha_only_if_audio captcha">Enter numbers you
hear:</label>
</td>
</tr>
<tr>
<td>
<input type="text" onblur="var wcall=wicketAjaxPost('../../../?
wicket:interface=:
5:content:comment:commentContainer:commentForm:rc:recaptcha_response_field::IBehaviorListener:
0:3', wicketSerialize(Wicket.$('recaptcha_response_field')),function()
{ }.bind(this),function() { }.bind(this), function() {return Wicket.$
('recaptcha_response_field') != null;}.bind(this));" value=""
name="rc:recaptcha_response_field" id="recaptcha_response_field"
class="input">
</td>
<td>
<a href="javascript:Recaptcha.reload()"><img width="25" height="17"
alt="Get a new challenge" src="
http://api.recaptcha.net/img/white/
refresh.gif" id="recaptcha_reload"></a>
<a href="javascript:Recaptcha.switch_type('audio')"
class="recaptcha_only_if_image"><img width="25" height="16"
src="
http://api.recaptcha.net/img/white/audio.gif"
id="recaptcha_switch_audio" alt="Get an audio challenge"></a>
<a title="Get a visual challenge"
href="javascript:Recaptcha.switch_type('image');"
id="recaptcha_switch_img_btn" class="recaptcha_only_if_audio"><img
width="25" height="16" src="
http://api.recaptcha.net/img/white/
text.gif" id="recaptcha_switch_img" alt="Get a visual challenge"></a>
<a href="javascript:Recaptcha.showhelp()"><img width="25" height="16"
alt="Help" src="
http://api.recaptcha.net/img/white/help.gif"
id="recaptcha_whatsthis"></a>
</td>
</tr>
<tr>
<td colspan="2"><span id="recaptcha__response__field__fp17">
</span></td>
</tr>
</tbody></table>
</div>
<script src="
http://api.recaptcha.net/challenge?k=null" type="text/
javascript" language="JavaScript"></script>Input error: k: Format of
site key was invalid
<noscript>
<iframe src="
http://api.recaptcha.net/noscript?k=null" 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>
</div>
</pre>