1 string chkCode = string.Empty;
 2 
 3 //颜色列表，用于验证码、噪线、噪点
 4 
 5 Color[] color = { Color.Black, Color.Red, Color.Blue, Color.Green, Color.Brown, Color.Brown, Color.DarkBlue };
 6 
 7 //字体列表，用于验证码
 8 
 9 string[] font = { "Gungsuh" };
10 
11 //验证码的字符集，去掉了一些容易混淆的字符
12 
13 char[] character = { '2', '3', '4', '5', '6', '8', '9', 'A', 'B', 'C', 'D', 'E', 'F', 'G', 'H', 'J', 'K', 'L', 'M', 'N', 'P', 'R', 'S', 'T', 'W', 'X', 'Y' }; Random rnd = new Random();
14 
15 //生成验证码字符串
16 
17 for (int i = 0; i < 4; i++) { chkCode += character[rnd.Next(character.Length)]; } Bitmap bmp = new Bitmap(100, 40); Graphics g = Graphics.FromImage(bmp); g.Clear(Color.White);
18 
19 //画验证码字符串
20 
21 for (int i = 0; i < chkCode.Length; i++) { string fnt = font[rnd.Next(font.Length)]; Font ft = new Font(fnt, 22); Color clr = color[rnd.Next(color.Length)]; g.DrawString(chkCode[i].ToString(), ft, new SolidBrush(clr), (float)i * 20 + 8, (float)8); }
22 
23 //清除该页输出缓存，设置该页无缓存
24 
25 Response.Buffer = true; Response.ExpiresAbsolute = System.DateTime.Now.AddMilliseconds(0); Response.Expires = 0; Response.CacheControl = "no-cache"; Response.AppendHeader("Pragma", "No-Cache");
26 
27 //将验证码图片写入内存流，并将其以 "image/Png" 格式输出
28 
29 MemoryStream ms = new MemoryStream();
30 
31 try { bmp.Save(ms, ImageFormat.Png);
32 
33 Session["CheckCode"] = chkCode; Response.ClearContent();
34 
35 Response.ContentType = "image/Png"; Response.BinaryWrite(ms.ToArray()); } finally {
36 
37 //显式释放资源
38 
39 bmp.Dispose();
40 
41 g.Dispose(); }