mvc generate captcha after failed login attempt
<% using(Html.BeginForm()) {%>
      <%: Html.AntiForgeryToken() %>
      <%: Html.ValidationSummary() %>
      <label>Username:</label>
      <%: Html.TextBoxFor(m => m.Username) %>
      <br /><br />
      <label>Password:</label>
      <%: Html.PasswordFor(m => m.Password) %>
      <br /><br />
      <input type="submit" value="Login" />
      <%: Html.ActionLink("Register", "Register", "") %>
      <%: Html.ActionLink("Forgot Password", "Password", "") %>
      <%: Html.ActionLink("Forgot Username", "Username", "") %>


      <%: ReCaptcha.GetHtml(publicKey: "thisismykey", theme: "red") %>


    <% } %>

<%: if (Model.NumberofFailedLogins > 3) { %>
<%: ReCaptcha.GetHtml(publicKey: "thisismykey", theme: "red") %>
<% } %>