asp.net產生字母和數字混合圖形驗證碼

具體實現方法如下：

1、主要思路是：引用Using System.Drawing命名空間，利用Graphics的FromImage方法建立一個畫布，同時設定畫布的寬和高，然後通過Graphics類 的DrawString方法隨機產生的字串繪製到畫布中，繪製驗證碼的同時，在畫布中利用SetPixel方法繪製一些色點，從而防止非法人員利用機器 人來進行登陸。當我們繪製驗證碼完畢後，在需要驗證碼的頁面中利用Image空間將其顯示出來，Image控制項顯示驗證碼的HTML源碼設定如下：

<asp:Image ID="Image1" runat="server"ImageUrl="~/ValidateNum.aspx" /><asp:LinkButton ID="LinkButton1" runat="server" style="font-size: small; ">看不清，換一張</asp:LinkButton>

2、這裡所用到的ValidateNum.aspx頁面代碼如下：

using System;using System.Collections;using System.Configuration;using System.Data;using System.Linq;using System.Web;using System.Web.Security;using System.Web.UI;using System.Web.UI.HtmlControls;using System.Web.UI.WebControls;using System.Web.UI.WebControls.WebParts;using System.Xml.Linq;using System.Drawing; public partial class ValidateNum : System.Web.UI.Page{  protected void Page_Load(object sender, EventArgs e)  {    if (!IsPostBack)    {      string validateNum = CreateRandomNum(4);//成生4位隨機字串      CreateImage(validateNum);//將產生的隨機字串繪成圖片      Session["ValidateNum"] = validateNum;//儲存驗證碼    }  }  //產生隨機字串  private string CreateRandomNum(int NumCount)  {    string allChar = "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,W,X,Y,Z";    string[] allCharArray = allChar.Split(',');//拆分成數組    string randomNum = "";    int temp = -1;//記錄上次隨機數的數值，盡量避免產生幾個相同的隨機數     Random rand = new Random();    for (int i = 0; i < NumCount; i++)    {      if (temp != -1)      {        rand = new Random(i * temp * ((int)DateTime.Now.Ticks));      }      int t = rand.Next(35);      if (temp == t)      {        return CreateRandomNum(NumCount);      }      temp = t;      randomNum += allCharArray[t];    }    return randomNum;  }  //產生圖片  private void CreateImage(string validateNum)  {    if (validateNum == null || validateNum.Trim() == String.Empty)      return;    //產生Bitmap映像    System.Drawing.Bitmap image = new System.Drawing.Bitmap(validateNum.Length * 12 + 10, 22);    Graphics g = Graphics.FromImage(image);     try    {      //產生隨機產生器      Random random = new Random();       //清空圖片背景色      g.Clear(Color.White);       //畫圖片的背景雜音線      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(validateNum, 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()));      }       //畫圖片的邊框線      g.DrawRectangle(new Pen(Color.Silver), 0, 0, image.Width - 1, image.Height - 1);       System.IO.MemoryStream ms = new System.IO.MemoryStream();      //將映像儲存到指定的流      image.Save(ms, System.Drawing.Imaging.ImageFormat.Gif);      Response.ClearContent();      Response.ContentType = "image/Gif";      Response.BinaryWrite(ms.ToArray());    }    finally    {      g.Dispose();      image.Dispose();    }  }}

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