1 private void Page_Load(object sender, System.EventArgs e)
2     {
3         this.CreateCheckCodeImage(GenerateCheckCode());
4     }
5
6     #region 生成4位随机数
7     private string GenerateCheckCode()
8  {
9   int number;
10   char code;
11   string checkCode = String.Empty;
12   System.Random random = new Random();
13   for(int i=0; i<4; i++)
14   {
15    number = random.Next();
16
17    if(number % 2 == 0)
18             {
19     code = (char)('0' + (char)(number % 10));
20             }
21    else
22             {
23     code = (char)('A' + (char)(number % 26));
24             }
25
26    code = (char)('0' + (char)(number % 10));
27
28    checkCode += code.ToString();
29   }
30   HttpContext.Current.Session["CheckCode"]=checkCode;
31   return checkCode;
32     }
33     #endregion
34
35     #region 生成验证码图片
36     private void CreateCheckCodeImage(string checkCode)
37  {
38   if(checkCode == null || checkCode.Trim() == String.Empty)
39         {
40    return;
41         }
42   Bitmap image = new Bitmap((int)Math.Ceiling((checkCode.Length * 12.5)), 22);
43   Graphics g = Graphics.FromImage(image);
44   try
45   {
46    //生成随机生成器
47    Random random = new Random();
48
49    //清空图片背景色
50    g.Clear(Color.White);
51
52    //画图片的背景噪音线
53    for(int i=0; i<25; i++)
54    {
55     int x1 = random.Next(image.Width);
56     int x2 = random.Next(image.Width);
57     int y1 = random.Next(image.Height);
58     int y2 = random.Next(image.Height);
59
60     g.DrawLine(new Pen(Color.Silver), x1, y1, x2, y2);
61    }
62
63    Font font = new Font("Arial", 12, (FontStyle.Bold | FontStyle.Italic));
64    LinearGradientBrush brush = new LinearGradientBrush(new Rectangle(0, 0, image.Width, image.Height), Color.Blue, Color.DarkRed, 1.2f, true);
65    g.DrawString(checkCode, font, brush, 2, 2);
66
67    //画图片的前景噪音点
68    for(int i=0; i<100; i++)
69    {
70     int x = random.Next(image.Width);
71     int y = random.Next(image.Height);
72
73     image.SetPixel(x, y, Color.FromArgb(random.Next()));
74    }
75
76    //画图片的边框线
77    g.DrawRectangle(new Pen(Color.Silver), 0, 0, image.Width - 1, image.Height - 1);
78    MemoryStream ms = new MemoryStream();
79    image.Save(ms,ImageFormat.Gif);
80    Response.ClearContent();
81    Response.ContentType = "image/Gif";
82    Response.BinaryWrite(ms.ToArray());
83   }
84   finally
85   {
86    g.Dispose();
87    image.Dispose();
88   }
89     }
90     #endregion
91
92     public static bool CheckCode(string strCode)
93     {
94         strCode = strCode.ToUpper();
95         string strSessionCode = HttpContext.Current.Session["CheckCode"] + "";
96         strSessionCode = strSessionCode.ToUpper();
97         System.Web.HttpContext.Current.Session["CheckCode"] = null;//注意要清空，防止一个session时间内攻击
98         return (strSessionCode == strCode);
99     }