public class ValidationCode : IHttpHandler 
{ 
//隨機發生器 
static Random r = new Random(Guid.NewGuid().GetHashCode()); 
//排除黑色、透明色顏色，因為底色黑色 
static PropertyInfo[] colors = (typeof(Brushes).GetProperties(System.Reflection.BindingFlags.Public | System.Reflection.BindingFlags.GetProperty | System.Reflection.BindingFlags.Static)).Where(p => p.Name != "Black" && p.Name != "Transparent").Select(p => p).ToArray(); 
//排除黑色顏色，因為底色黑色 
static PropertyInfo[] linecolors = (typeof(Pens).GetProperties(System.Reflection.BindingFlags.Public | System.Reflection.BindingFlags.GetProperty | System.Reflection.BindingFlags.Static)).Where(p => p.Name != "Black").Select(p => p).ToArray(); 
//獲取靜態類Brushes實例對象 
static object colorobj = typeof(Brushes).GetConstructor(BindingFlags.NonPublic, null, Type.EmptyTypes, null); 
//獲取靜態類Pens實例對象 
static object penobj = typeof(Pens).GetConstructor(BindingFlags.NonPublic, null, Type.EmptyTypes, null); 
//每個隨機字符的寬度 
const float PERNUMBERWIDTH = 40.0f; 
//每個字符的高度 
const float PERNUMBERHEIGHT = 50.0f; 
public void ProcessRequest(HttpContext context) 
{ 
//獲取要產生多少隨機數（默認產生5個） 
int reqNum = 5; 
if (context.Request.QueryString["reqNum"] != null) 
{ 
int.TryParse(context.Request.QueryString["reqNum"], out reqNum); 
} 
//產生多少大的背景圖 
Bitmap bt = new Bitmap((int)(PERNUMBERWIDTH*reqNum), (int)PERNUMBERHEIGHT); 
Graphics g = Graphics.FromImage(bt); 
//產生4個隨機數（number可以被保存到Session中） 
string numbers = ""; 
//繪制數字 
for (int i = 1; i <= reqNum; i++) 
{ 
numbers += r.Next(0, 9).ToString(); 
var color = (PropertyInfo)colors.GetValue(r.Next(0, colors.Length)); 
context.Response.Write(color.Name + "<br/>"); 
Brush randomcolor = (Brush)color.GetValue(colorobj, null); 
g.DrawString(numbers[i-1].ToString(), new Font("黑體", PERNUMBERWIDTH),randomcolor, new PointF((i-1)*PERNUMBERWIDTH, 0f)); 
} 
//繪制隨機線條 
int linenum = r.Next(10, 21); 
for (int i = 1; i <= linenum; i++) 
{ 
var linecolor = (PropertyInfo)linecolors.GetValue(r.Next(0, colors.Length)); 
Pen randomcolor = (Pen)linecolor.GetValue(penobj, null); 
g.DrawLine(randomcolor, new PointF((float)(r.NextDouble() * PERNUMBERWIDTH * reqNum), (float)(r.NextDouble() * PERNUMBERHEIGHT)), new PointF((float)(r.NextDouble() * PERNUMBERWIDTH * reqNum), (float)(r.NextDouble() * PERNUMBERHEIGHT))); 
} 
g.Dispose(); 
context.Response.Clear(); 
context.Response.ContentType = "image/jpeg"; 
bt.Save(context.Response.OutputStream, ImageFormat.Jpeg); 
bt.Dispose(); 
context.Response.End(); 
} 
public bool IsReusable 
{ 
get 
{ 
return false; 
} 
} 
} 
 
[VB.NET] 
 代碼如下:

Public Class ValidationCode 
Implements IHttpHandler 
'隨機發生器 
Shared r As New Random(Guid.NewGuid().GetHashCode()) 
'排除黑色、透明色顏色，因為底色黑色 
Shared colors As PropertyInfo() = (GetType(Brushes).GetProperties(System.Reflection.BindingFlags.[Public] Or System.Reflection.BindingFlags.GetProperty Or System.Reflection.BindingFlags.[Static])).Where(Function(p) p.Name <> "Black" AndAlso p.Name <> "Transparent").[Select](Function(p) p).ToArray() 
'排除黑色顏色，因為底色黑色 
Shared linecolors As PropertyInfo() = (GetType(Pens).GetProperties(System.Reflection.BindingFlags.[Public] Or System.Reflection.BindingFlags.GetProperty Or System.Reflection.BindingFlags.[Static])).Where(Function(p) p.Name <> "Black").[Select](Function(p) p).ToArray() 
'獲取靜態類Brushes實例對象 
Shared colorobj As Object = GetType(Brushes).GetConstructor(BindingFlags.NonPublic, Nothing, Type.EmptyTypes, Nothing) 
'獲取靜態類Pens實例對象 
Shared penobj As Object = GetType(Pens).GetConstructor(BindingFlags.NonPublic, Nothing, Type.EmptyTypes, Nothing) 
'每個隨機字符的寬度 
Const PERNUMBERWIDTH As Single = 40F 
'每個字符的高度 
Const PERNUMBERHEIGHT As Single = 50F 
Public Sub ProcessRequest(context As HttpContext) 
'獲取要產生多少隨機數（默認產生5個） 
Dim reqNum As Integer = 5 
If context.Request.QueryString("reqNum") IsNot Nothing Then 
Integer.TryParse(context.Request.QueryString("reqNum"), reqNum) 
End If 
'產生多少大的背景圖 
Dim bt As New Bitmap(CInt(Math.Truncate(PERNUMBERWIDTH * reqNum)), CInt(Math.Truncate(PERNUMBERHEIGHT))) 
Dim g As Graphics = Graphics.FromImage(bt) 
'產生4個隨機數（number可以被保存到Session中） 
Dim numbers As String = "" 
'繪制數字 
For i As Integer = 1 To reqNum 
numbers += r.[Next](0, 9).ToString() 
Dim color = DirectCast(colors.GetValue(r.[Next](0, colors.Length)), PropertyInfo) 
context.Response.Write(Convert.ToString(color.Name) & "<br/>") 
Dim randomcolor As Brush = DirectCast(color.GetValue(colorobj, Nothing), Brush) 
g.DrawString(numbers(i - 1).ToString(), New Font("黑體", PERNUMBERWIDTH), randomcolor, New PointF((i - 1) * PERNUMBERWIDTH, 0F)) 
Next 
'繪制隨機線條 
Dim linenum As Integer = r.[Next](10, 21) 
For i As Integer = 1 To linenum 
Dim linecolor = DirectCast(linecolors.GetValue(r.[Next](0, colors.Length)), PropertyInfo) 
Dim randomcolor As Pen = DirectCast(linecolor.GetValue(penobj, Nothing), Pen) 
g.DrawLine(randomcolor, New PointF(CSng(r.NextDouble() * PERNUMBERWIDTH * reqNum), CSng(r.NextDouble() * PERNUMBERHEIGHT)), New PointF(CSng(r.NextDouble() * PERNUMBERWIDTH * reqNum), CSng(r.NextDouble() * PERNUMBERHEIGHT))) 
Next 
g.Dispose() 
context.Response.Clear() 
context.Response.ContentType = "image/jpeg" 
bt.Save(context.Response.OutputStream, ImageFormat.Jpeg) 
bt.Dispose() 
context.Response.[End]() 
End Sub 
Public ReadOnly Property IsReusable() As Boolean 
Get 
Return False 
End Get 
End Property 
End Class 
 
注意： 
1）一些諸如Brushes等特定因為是公用的，需要通過反射獲取全部的顏色屬性列表，因此使用了靜態變量，這樣不必每次都初始化，節省內存和時間。 
2）Brushes避免黑色和透明色（本示例背景色是黑色），Pens只需避免黑色即可。有關Brushes顏色，可以查閱：http://msdn.microsoft.com/zh-cn/library/system.windows.media.brush(v=vs.95).aspx 
3）Bitmap類是用于繪制使用的，一般是空白的黑色背景。一般配合Image類+Graphics畫布使用，進行繪制。 
4）BitMap的Save方法有若干個重載版本，其中之一可以指定