protected void Page_Load(object sender, EventArgs e) 
{ 
//獲取GB2312編碼頁（表） 
/**//** 
* 生成中文驗證驗碼所要使用的方法 
* 注，生成中文驗證碼時要改變一下生成驗證碼圖片的寬度 
* var imageCode = new System.Drawing.Bitmap((int)Math.Ceiling((code.Length * 22.5)), 23); //定義圖片的寬度和高度 
**/ 

//var gb = Encoding.GetEncoding("gb2312"); 

/**/////調用函數產生4個隨機中文漢字編碼 
//object[] bytes = CreateRegionCode(4); 

/**/////根據漢字編碼的字節數組解碼出中文漢字 
//var sbCode = new StringBuilder().Append(gb.GetString((byte[])Convert.ChangeType(bytes[0], typeof(byte[])))) 
// .Append(gb.GetString((byte[])Convert.ChangeType(bytes[1], typeof(byte[])))) 
// .Append(gb.GetString((byte[])Convert.ChangeType(bytes[2], typeof(byte[])))) 
// .Append(gb.GetString((byte[])Convert.ChangeType(bytes[3], typeof(byte[])))); 
//CreateCheckCodeImage(sbCode.ToString()); 

CreateCheckCodeImage(GenerateCheckCode()); //生成數字英文所要使用的方法 
} 

生成漢字驗證碼#region 生成漢字驗證碼 
/**//// <summary> 
/// 此函數在漢字編碼范圍內隨機創建含兩個元素的十六進制字節數組，每個字節數組代表一個漢字，并將四個字節數組存儲在object數組中。 
/// </summary> 
/// <param name="strLength">代表需要產生的漢字個數</param> 
/// <returns></returns> 
static object[] CreateRegionCode(int strLength) 
{ 
var rBase = new[] 
{ 
"0","1","2","3","4","5","6","7","8","9","a","b","c","d","e","f" 
}; 

var random = new Random(); 
var bytes = new object[strLength]; 

/**//*每循環一次產生一個含兩個元素的十六進制字節數組，并將其放入bject數組中 
每個漢字有四個區位碼組成 
區位碼第1位和區位碼第2位作為字節數組第一個元素 
區位碼第3位和區位碼第4位作為字節數組第二個元素 
*/ 

for (int i = 0; i < strLength; i++) 
{ 
//區位碼第1位 
var r1 = random.Next(11, 14); 
var str_r1 = rBase[r1].Trim(); 

random = new Random(r1 * unchecked((int)DateTime.Now.Ticks) + i); //更換隨機數發生器的種子避免產生重復值 

var r2 = 0; 
if (r1 == 13) 
r2 = random.Next(0, 7); 
else 
r2 = random.Next(0, 16); 

var str_r2 = rBase[r2].Trim(); 

//區位碼第3位 
random = new Random(r2 * unchecked((int)DateTime.Now.Ticks) + i); 
var r3 = random.Next(10, 16); 
var str_r3 = rBase[r3].Trim(); 

//區位碼第4位 
random = new Random(r3 * unchecked((int)DateTime.Now.Ticks) + i); 
var r4 = 0; 
if (r3 == 10) 
r4 = random.Next(1, 16); 
else if (r3 == 15) 
r4 = random.Next(0, 15); 
else 
r4 = random.Next(0, 16); 

var str_r4 = rBase[r4].Trim(); 

var byte1 = Convert.ToByte(str_r1 + str_r2, 16); 
var byte2 = Convert.ToByte(str_r3 + str_r4, 16); 
//將兩個字節變量存儲在字節數組中 
var str_r = new[] { byte1, byte2 }; 

//將產生的一個漢字的字節數組放入object數組中 
bytes.SetValue(str_r, i); 
} 
return bytes; 
} 
#endregion 

生成圖片#region 生成圖片 
void CreateCheckCodeImage(string code) 
{ 
var imageCode = new System.Drawing.Bitmap((int)Math.Ceiling((code.Length * 12.5)), 23); //定義圖片的寬度和高度 
var g = Graphics.FromImage(imageCode); //加載圖片到畫布上 

try 
{ 
var random = new Random(); 
g.Clear(Color.White); //清空圖片背景色 

//畫圖片的背景噪音線 
for (int i = 0; i < 25; i++) 
{ 
var x1 = random.Next(imageCode.Width); 
var x2 = random.Next(imageCode.Width); 
var y1 = random.Next(imageCode.Height); 
var y2 = random.Next(imageCode.Height); 

g.DrawLine(new Pen(Color.Silver), new Point(x1, y1), new Point(x2, y2)); 
} 

var font = new System.Drawing.Font("Arial", 12F, System.Drawing.FontStyle.Bold | System.Drawing.FontStyle.Italic); 
var brush = new System.Drawing.Drawing2D.LinearGradientBrush( 
new Rectangle(0, 0, imageCode.Width, imageCode.Height), 
Color.Blue, Color.DarkRed, 1.2F, true); 
g.DrawString(code, font, brush, 2, 2); 

//畫圖片的前景噪音點 
for (int i = 0; i < 100; i++) 
{ 
var x = random.Next(imageCode.Width); 
var y = random.Next(imageCode.Height); 
imageCode.SetPixel(x, y, Color.FromArgb(random.Next())); 
} 

//畫圖片的邊框線 
g.DrawRectangle(new Pen(Color.Silver), 0, 0, imageCode.Width - 1, imageCode.Height - 1); 
var ms = new System.IO.MemoryStream(); 
imageCode.Save(ms, System.Drawing.Imaging.ImageFormat.Jpeg); 

Response.ClearContent(); 
Response.ContentType = "image/Jpeg"; 
Response.BinaryWrite(ms.ToArray()); 
} 
finally 
{ 
g.Dispose(); 
imageCode.Dispose(); 
} 

} 
#endregion 

生成數據驗證碼#region 生成數據驗證碼 
private string GenerateCheckCode() 
{ 
int number; 
char code; 
string checkCode = String.Empty; 

var random = new Random(); 

for (int i = 0; i < 5; i++) 
{ 
number = random.Next(); 

if (number % 2 == 0) 
code = (char)('0' + (char)(number % 10)); 
else 
code = (char)('A' + (char)(number % 26)); 

checkCode += code.ToString(); 
} 
return checkCode; 
} 
#endregion 
 

<form id="formCode" runat="server"> 
<div> 
<img src="CheckCode.aspx" src="CheckCode.aspx" alt="驗證碼" /> 
</div> 
</form>