C# 驗證碼

using System.Drawing;
using System.IO;
using System.Web.UI.WebControls;
using System.Web.UI.WebControls.WebParts;
using System.Web.UI.HtmlControls;

protected void Page_Load(object sender, EventArgs e)
{
    string str_ValidateCode = GetRandomNumberString(5);
    Session["ValidateCode"] = str_ValidateCode;    //驗證號碼存入session
    CreateCheckCodeImage(str_ValidateCode);

}

//亂數產生數字
private string GetRandomNumberString(int int_NumberLength)
{
    Random rnd = new Random();
    string RandonStr = "";

    for (int i = 0; i < int_NumberLength; i++)
    {
        RandonStr += rnd.Next(1, 9).ToString();
    }

    return RandonStr;
}

//動態建立圖片
private void CreateCheckCodeImage(string checkCode)
{
    Bitmap image = new Bitmap((int)(Math.Ceiling((checkCode.Length * 13.5))) , 25);
    Graphics g = Graphics.FromImage(image);

    Random random = new Random();
    g.Clear(Color.White);

    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", 14, (FontStyle.Bold));
    var 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);

    //畫圖片的前景噪音點
    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()));
    }

    string savePath = Server.MapPath("~") + "/images/validate.gif";   //圖片存放位子
    image.Save(savePath, System.Drawing.Imaging.ImageFormat.Gif);
     

}