验证码图片生成代码

    using System.Drawing;



    public partial class Pub_validcode : System.Web.UI.Page

    {

    protected void Page_Load(object sender, EventArgs e)

    {

        this.CreateCheckCodeImage(GenerateCheckCode());

    }



    //生成随机数

    private string GenerateCheckCode()

    {

        int number;

        char code;

        string checkCode = String.Empty;



        System.Random random = new Random();



        for (int i = 0; i < 4; i++)

        {

            number = random.Next();



            if (number % 2 == 0)

                code = (char)('0' + (char)(number % 10));

            else

                code = (char)('0' + (char)(number % 10));

            //code = (char)('a' + (char)(number % 26));



            checkCode += code.ToString();

        }



        Response.Cookies.Add(new HttpCookie("CheckCode", checkCode));



        //将生成的随机数保存到session中



        Session["Num"] = checkCode.ToString().ToLower();



        return checkCode;

    }



    private void CreateCheckCodeImage(string checkCode)

    {

        if (checkCode == null || checkCode.Trim() == String.Empty)

            return;



        System.Drawing.Bitmap image = new System.Drawing.Bitmap((int)Math.Ceiling((checkCode.Length * 12.5)), 22);

        Graphics g = Graphics.FromImage(image);



        try

        {

            //生成随机生成器 

            Random random = new Random();



            //清空图片背景色 

            g.Clear(Color.White);



            //画图片的背景噪音线 

            for (int i = 0; i < 25; i++)

            {

                int x1 = random.Next(image.Width);

                int x2 = random.Next(image.Width);

                int y1 = random.Next(image.Height);

                int y2 = random.Next(image.Height);



                g.DrawLine(new Pen(Color.Silver), x1, y1, x2, y2);

            }



            Font font = new System.Drawing.Font("Arial", 12, (System.Drawing.FontStyle.Bold | System.Drawing.FontStyle.Italic));

            System.Drawing.Drawing2D.LinearGradientBrush brush = new System.Drawing.Drawing2D.LinearGradientBrush(new Rectangle(0, 0, image.Width, image.Height), Color.Blue, Color.DarkRed, 1.2f, true);

            g.DrawString(checkCode, font, brush, 2, 2);



            //画图片的前景噪音点 

            for (int i = 0; i < 100; i++)

            {

                int x = random.Next(image.Width);

                int y = random.Next(image.Height);



                image.SetPixel(x, y, Color.FromArgb(random.Next()));

            }



            //画图片的边框线 

            g.DrawRectangle(new Pen(Color.Silver), 0, 0, image.Width - 2, image.Height - 1);



            System.IO.MemoryStream ms = new System.IO.MemoryStream();

            image.Save(ms, System.Drawing.Imaging.ImageFormat.Gif);

            Response.ClearContent();

            Response.ContentType = "image/Gif";

            Response.BinaryWrite(ms.ToArray());

        }

        finally

        {

            g.Dispose();

            image.Dispose();

        }

    }

} 

function refresh()

{    

    $("imgValid").src="ValidCode.aspx?temp="+ (new Date().getTime().toString(36)); 

    return false;

}

<img id="imgValid" src="ValidCode.aspx" onclick="javascript:refresh();" alt =""/>