How to add and validate google captche in dnn page - dotnetnuke

Question

I have work on dnn 7.1 .I have add the Google catcha in DNN page.
see reference from this site
code for add captcha in asp.net
with the help of this reference i have add the captcha in dnn page. but in the captcha validation is not work. anything write in the text box. not show the error message. and form submit successfully . Any one help me what can i do for validation.
code are given below
<%--<%# Register TagPrefix="recaptcha" Namespace="Recaptcha" Assembly="Recaptcha" %>--%>
<%# Control Language="C#" ClassName="Admin.ContactUs" Inherits="DotNetNuke.Entities.Modules.PortalModuleBase" %>
<%# Import Namespace="System" %>
<%# Import Namespace="System.Collections" %>
<%# Import Namespace="System.Configuration" %>
<%# Import Namespace="System.Data" %>
<script runat="server">
protected void btnSubmit_Click(object sender, EventArgs e)
{
if (Page.IsValid)
{
SendMailTest();
}
else
{
}
}
protected void Page_Load(object sender, EventArgs e)
{
}
</script>
<div class="contactusform-left commonclass lF">
<asp:Label ID="lblmsg" runat="server" Text=""></asp:Label>
/* Code for textbox, dropdowm */
</div>
<div class="contactusform-right commonclass lF">
<div class="contactusform-set-textarea contactusform-set" style="height:150px;">
<label class="lF">
Captcha <span>*</span></label>
<div style="clear:left;width:100%;height:100px;">
<recaptcha:RecaptchaControl ID="recaptcha" runat="server" PublicKey="6LdCxeYSAAAAAAP-uIGWnsZHeW7rn8rzeeblc5g"
PrivateKey="6LdCxeYSAAAAAFvnxCiaN_7vkHp-vaVRRYb9yVF" />
<asp:Label Visible=false ID="lblResult" runat="server" />
</div>
</div>
<div style="clear:both;"></div>
<div class="contactusform-set " style="margin-top:10px;">
<asp:Button ID="btnSubmit" runat="server" Text="Submit" OnClick="btnSubmit_Click"
ValidationGroup="ContactUsValidate" />
<asp:Button ID="btnCancel" runat="server" Text="Cancel" Style="color: #8D8D8D; cursor: pointer;
float: right; font-weight: bold; height: 34px; margin-right: 5px; text-transform: uppercase;
width: 120px;" />
</div>
</div>

Answer 1

Without sample code it will be very hard to give you a valid answer here, but the most common cause of it would be if you are using a "ValidationGroup" on the button or other controls, but not on the CAPTCHA.
Otherwise, we need to see your specific code.

Answer 2

Do you know that DotNetNuke provides the Telerik captcha control? You can use it exactly as described here: http://demos.telerik.com/aspnet-ajax/captcha/examples/overview/defaultcs.aspx but you just need to replace radCaptcha by dnnCaptcha in your code and add these two lines at the beginning of your file:
<%# Register TagPrefix="dnn" Namespace="DotNetNuke.UI.WebControls" Assembly="DotNetNuke" %>
<%# Register TagPrefix="dnn" Namespace="DotNetNuke.Web.UI.WebControls" Assembly="DotNetNuke.Web" %>