圖片驗證碼

drawimg.aspx.cs(片段)
private void Page_Load(object sender, System.EventArgs e)
  {
   // 在這裡放置使用者程式碼以初始化網頁
   string valCode = RandomString(int.Parse("7"));
   Session.Add("ValCode", valCode);
   DrawImage(valCode);

  }
  private string RandomString(int bit)
  {
   string chars = "0,1,2,3,4,5,6,7,8,9,A,B,C,D,E,F,G,H,I,J,K,L,M,N,O,P,Q,R,S,T,U,V,W,X,Y,Z" ;
   string[] charArray = chars.Split(',');
   string result = "";
   Random rdm = new Random();
   for (int i = 0; i < bit; i++)
   {
    result += charArray[rdm.Next(36)];
   }
   return result;
  }

  //?????成?形
  private void DrawImage(string valCode)
  {
   //生成位?
   Bitmap bmp = new Bitmap(valCode.Length*20, 25);
   Graphics g = Graphics.FromImage(bmp);
   try
   {
    g.Clear(Color.White);

    //定義色和字体集
    Color[] c = {Color.Red, Color.Green, Color.Navy, Color.DarkCyan, Color.Blue, Color.Purple};
    string[] fonts = {"Microsoft Sans Serif", "Times New Roman", "Lucida Console", "Arial", "Verdana"};

    //制背景网格
    Pen p = new Pen(Color.LightGray, 0);
    int y = 5;
    do
    {
     g.DrawLine(p, 0, y, bmp.Width, y);
     y += 5;
    }
    while(y < bmp.Height);
    int x = 5;
    do
    {
     g.DrawLine(p, x, 0, x, bmp.Height);
     x += 5;
    }
    while(x < bmp.Width);

   
    Random rdm = new Random();
    for (int i = 0; i < valCode.Length; i++)
    {
     int ci = rdm.Next(c.Length);
     int fi = rdm.Next(fonts.Length);
     Font f = new Font(fonts[fi], 12, FontStyle.Bold);
     Brush b = new SolidBrush(c[ci]);
     g.DrawString(valCode.Substring(i,1), f, b, 5+(i*14), rdm.Next(2,5));
    }

        g.DrawRectangle(p, 0, 0, bmp.Width-1, bmp.Height-1);

    
    MemoryStream ms = new MemoryStream();
    bmp.Save(ms, System.Drawing.Imaging.ImageFormat.Gif);
    Response.Cache.SetNoStore();
    Response.ClearContent();
    Response.ContentType = "image/Gif";
    Response.BinaryWrite(ms.ToArray());
    Response.End();
   }


這樣用：

<img = "drawimg.aspx">