C# 实现验证码代码示例

 protected void Page_Load(object sender, EventArgs e)
    {
        string checkCodeString = "0123456789AaBbCcDdEeFfGgHhIiJjKkLlMmNnOoPpQqRrSsTtUuVvWwXxYyZz";//验证码中可能会出现的字符集合
        int lenth = checkCodeString.Length;//验证码字符集合的长度
        //设置以宋体来绘制验证码字符，并且设置绘制成粗体
        Font fnt = new Font("宋体", 10);
        Brush brush = null;//绘制验证码的Brush对象
        Color brushColor = new Color();//绘制验证码文字的颜色
        string checkCode = string.Empty;//整个显示给用户的验证码字符串
        string code = string.Empty;//当前要绘制的验证码字符
        Bitmap image = new Bitmap(80, 40);
        Graphics g = Graphics.FromImage(image);
        g.Clear(Color.White);


        Random random = new Random();
        for (int i = 0; i < 4; i++)
        {
            int current = random.Next(DateTime.Now.Millisecond) % lenth;
            code = checkCodeString.Substring(current, 1);
            brushColor = Color.FromArgb(random.Next(255), random.Next(255), random.Next(255));

            brush = new SolidBrush(brushColor);
            g.DrawString(code, fnt, brush, i * 15 + 2, 2);
        }
        Response.Clear();
        Response.ContentType = "images/";
        image.Save(Response.OutputStream, ImageFormat.Jpeg);
        Session["CheckCode"] = checkCode;
        image.Dispose();