C# ASP.NET登錄頁面驗證碼

根据提供的引用内容，以下是一个C# ASP.NET登录页面验证码的制作与校验的示例：

1. 在ASP.NET页面中添加一个Image控件用于显示验证码图片，并设置其ID为"imgCaptcha"。
2. 在后台代码中生成验证码图片，并将其保存到Session中以便校验。

protected void Page_Load(object sender, EventArgs e)
{
    if (!IsPostBack)
    {
        string captcha = GenerateCaptcha();
        Session["Captcha"] = captcha;
        imgCaptcha.ImageUrl = "GenerateCaptchaImage.aspx";
    }
}

private string GenerateCaptcha()
{
    // 生成随机验证码
    string captcha = GenerateRandomCode();

    // 将验证码绘制到图片上
    Bitmap image = new Bitmap(200, 80);
    Graphics graphics = Graphics.FromImage(image);
    graphics.DrawString(captcha, new Font("Arial", 40), Brushes.Black, new PointF(10, 10));

    // 添加噪点和干扰线条
    AddNoiseAndLines(graphics);

    // 保存图片并返回验证码
    string imagePath = Server.MapPath("~/CaptchaImages/captcha.png");
    image.Save(imagePath, ImageFormat.Png);
    return captcha;
}

private string GenerateRandomCode()
{
    // 生成随机验证码
    string characters = "0123456789ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz";
    Random random = new Random();
    StringBuilder captcha = new StringBuilder();
    for (int i = 0; i < 6; i++)
    {
        captcha.Append(characters[random.Next(characters.Length)]);
    }
    return captcha.ToString();
}

private void AddNoiseAndLines(Graphics graphics)
{
    // 添加噪点
    Random random = new Random();
    for (int i = 0; i < 100; i++)
    {
        int x = random.Next(graphics.VisibleClipBounds.Width);
        int y = random.Next(graphics.VisibleClipBounds.Height);
        graphics.FillRectangle(Brushes.Black, x, y, 1, 1);
    }

    // 添加干扰线条
    for (int i = 0; i < 10; i++)
    {
        int x1 = random.Next(graphics.VisibleClipBounds.Width);
        int y1 = random.Next(graphics.VisibleClipBounds.Height);
        int x2 = random.Next(graphics.VisibleClipBounds.Width);
        int y2 = random.Next(graphics.VisibleClipBounds.Height);
        graphics.DrawLine(Pens.Black, x1, y1, x2, y2);
    }
}

3. 创建一个名为"GenerateCaptchaImage.aspx"的新页面，用于生成验证码图片。

protected void Page_Load(object sender, EventArgs e)
{
    string captcha = Session["Captcha"] as string;
    if (!string.IsNullOrEmpty(captcha))
    {
        Bitmap image = new Bitmap(200, 80);
        Graphics graphics = Graphics.FromImage(image);
        graphics.DrawString(captcha, new Font("Arial", 40), Brushes.Black, new PointF(10, 10));
        AddNoiseAndLines(graphics);
        Response.ContentType = "image/png";
        image.Save(Response.OutputStream, ImageFormat.Png);
    }
}

private void AddNoiseAndLines(Graphics graphics)
{
    // 添加噪点和干扰线条的代码同上
}

4. 在登录页面中添加一个TextBox控件用于输入验证码，并设置其ID为"txtCaptcha"，以及一个Button控件用于提交表单，并设置其ID为"btnSubmit"。
5. 在后台代码中校验验证码。

protected void btnSubmit_Click(object sender, EventArgs e)
{
    string captcha = Session["Captcha"] as string;
    string inputCaptcha = txtCaptcha.Text.Trim();
    if (!string.IsNullOrEmpty(captcha) && !string.IsNullOrEmpty(inputCaptcha))
    {
        if (captcha.Equals(inputCaptcha, StringComparison.OrdinalIgnoreCase))
        {
            // 验证码输入正确
            // 执行登录逻辑
        }
        else
        {
            // 验证码输入错误
            // 提示用户重新输入验证码
        }
    }
}