現在很多網頁登陸的時候都使用了隨機圖片的方式，是一種簡單、有效的防止駭客惡意攻擊的手段。今天看了一些網路上的資料，明白其產生原理：從樣本中，取得隨機字串，隨機字串儲存進session，並以點陣圖的方式形成隨機碼圖片。
實現：
新增命名空間
using System.Drawing;
using System.Drawing.Imaging;
using System.Drawing.Drawing2D;
生成頁碼
using System;
using System.Data;
using System.Configuration;
using System.Collections;
using System.Web;
using System.Web.Security;
using System.Web.UI;
using System.Web.UI.WebControls;
using System.Web.UI.WebControls.WebParts;
using System.Web.UI.HtmlControls;
using System.Drawing;
using System.Drawing.Imaging;
using System.Drawing.Drawing2D;
public partial class getRandImg : System.Web.UI.Page
{
protected void Page_Load(object sender, EventArgs e)
{
//產生隨機碼圖片
SetValidateCode();
//產生頁面不儲存到cache
Response.Cache.SetNoStore();
}
//設定驗證碼
private void SetValidateCode()
{
//新點陣圖
Bitmap newBitmap = new Bitmap(
71,
23,
PixelFormat.Format32bppArgb
);
//從點陣圖取得繪圖畫面
Graphics g = Graphics.FromImage(newBitmap);
//隨機數字產生器
Random r = new Random();
//繪圖畫面清空
g.Clear(Color.White);
//繪圖畫面劃線幹擾
for (int i = 0; i < 50; i++)
{
int x1 = r.Next(newBitmap.Width);
int x2 = r.Next(newBitmap.Width);
int y1 = r.Next(newBitmap.Height);
int y2 = r.Next(newBitmap.Height);
g.DrawLine(new Pen(
Color.FromArgb(r.Next())),
x1,
y1,
x2,
y2
);
}
//繪圖畫面點數幹擾
for (int i = 0; i < 100; i++)
{
int x = r.Next(newBitmap.Width);
int y = r.Next(newBitmap.Height);
newBitmap.SetPixel(
x,
y,
Color.FromArgb(r.Next())
);
}
//取得隨機字串（5位元長度）
string value = GenerateRandom(5);
//隨機字串賦值給Session
Session["RandCode"] = value;
//定義圖片顯示字體樣式
Font font = new Font(
"Arial",
14,
FontStyle.Bold
);
Random rr = new Random();
int yy = rr.Next(1, 4);
//定義隨機字串顯示圖片刷子
LinearGradientBrush brush = new LinearGradientBrush(
new Rectangle(0, 0, 71, 23),
Color.Red,
Color.Blue,
1.2f,
true
);
g.DrawString(value, font, brush, 2, yy);
g.DrawRectangle(new Pen(
Color.Silver),
0,
0,
70,
22
);
System.IO.MemoryStream ms = new System.IO.MemoryStream();
newBitmap.Save(ms, ImageFormat.Gif);
//輸出圖片
Response.ClearContent();
Response.ContentType = "image/gif";
Response.BinaryWrite(ms.ToArray());
}
//常數集
private static char[] constant ={
'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'
};
//產生隨機字串
public static string GenerateRandom(int Length)
{
System.Text.StringBuilder newRandom = new System.Text.StringBuilder(36);
Random rd = new Random();
for (int i = 0; i < Length; i++)
{
newRandom.Append(constant[rd.Next(36)]);
}
return newRandom.ToString();
}
}
使用隨機圖片的頁面，IMAGE控制項的寫法如下：
<asp:Image ID="Image1" ImageUrl="~/getRandImg.aspx" runat="server" /> 範例程式碼
：http: //www.cnblogs.com /heekui/archive/2007/01/06/613609.html