MVC2 and session

I'm making use of a captcha generator. http://xcaptcha.codeplex.com/. In the example it shows using Session.Add for comparing captcha generated vs answer. I wanted to make this a part of my model's rule violation checker but I can't seem to find/work with the correct parts of session there. Am I missing the way to navigate 开发者_运维百科to session from within my model's GetRuleViolations? Any other tips appreciated

// Controller
public ActionResult Image()
{
    var builder = new XCaptcha.ImageBuilder();
    var result = builder.Create();
    Session.Add("CaptchaKey", result.Solution);
    return new FileContentResult(result.Image, result.ContentType);
}

// My model
public IEnumerable<RuleViolation> GetRuleViolations()
{
    // This isn't correct... it isn't stored in server variables
    string captchaAnswer = HttpContext.Current.Request.ServerVariables.Get("CaptchaKey");
    // No such thing..
    string res = Session["Something"].ToString();
}

// My eh solution
// Controller
[HttpPost]
public ActionResult ContactUs(EmailModel e, FormCollection collection)
{
    string captchaAnswer = Session["CaptchaKey"].ToString();
    string captchaText = collection["CaptchaText"].ToUpper().ToString();
    bool correctCaptcha = (captchaAnswer.CompareTo(captchaText) == 0) ? true : false;

    if (e.IsValid && correctCaptcha)
    {
        EmailHelper.SendMessage(e);
        return RedirectToAction("ContactSuccess");
    }
    else
    {
        if (!correctCaptcha)
            ModelState.AddModelError("Captcha", "Incorrect Captcha answer");

        ModelState.AddRuleViolations(e.GetRuleViolations());
    }

    return View(e);
}

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HttpContext.Current.Session

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I've just updated it. There is now a version 2 which no longer uses sessions to maintain state and uses model-base validation.