这个程序主要是先生成一个随机数，然后根据生成的随机数经过变换后作为XBM图片的内容，最后显示这个图片. 验证时中要获取输入的数字和Session("validatecode")比较，如果相等则通过验证（还要注意一下相比较的两数据的类型保持一致）。

如何显示生成的图片呢？ <img src="xbm.asp"></img>

关于XBM图的格式信息，看这里
http://www.zdnet.com.cn/developer/tech/story/0,2000081602,39134972,00.htm

xbm.asp的代码如下
程序代码：
<!--#include file="numcode.asp"-->
<%
  '开启缓冲
Response.Buffer = True
With Response
 .Expires = -1
 .AddHeader "Pragma","no-cache"
 .AddHeader "cache-ctrol","no-cache"
End With

Dim num
Randomize
num = Int(7999 * Rnd + 2000)
Session("validateCode") = num

Dim Image
Dim Width, Height
Dim digtal
Dim Length
Dim sort
Dim hc
Length = 4
hc = chr(13) & chr(10)

Redim sort(Length)

digital = ""
For I = 1 To Length - Len(num)
 digital = digital & "0"
Next
For I = 1 To Len(num)
 digital = digital & Mid(num, I, 1)
Next
For I = 1 To Len(digital)
 sort(I) = Mid(digital, I, 1)
Next
Width = 8 * Len(digital)
Height = 10

Response.ContentType = "image/x-xbitmap"

Image = "#define counter_width " & Width & hc
Image = Image & "#define counter_height " & Height & hc
Image = Image & "static unsigned char counter_bits[] = {" & hc

For I = 1 To Height
 For J = 1 To Length
  Image = Image & a(sort(J),I) & ","
 Next
Next

Image = Left(Image, Len(Image) - 1)
Image = Image & "};" & hc

Response.Write Image
%>

Numcode.asp的代码如下：
程序代码：
<%
  Dim a(10,10)
  a(0,1) = "0x3c" '数字0
  a(0,2) = "0x66"
  a(0,3) = "0xc3"
  a(0,4) = "0xc3"
  a(0,5) = "0xc3"
  a(0,6) = "0xc3"
  a(0,7) = "0xc3"
  a(0,8) = "0xc3"
  a(0,9) = "0x66"
  a(0,10)= "0x3c"
  a(1,1) = "0x18" '数字1
  a(1,2) = "0x1c"
  a(1,3) = "0x18"
  a(1,4) = "0x18"
  a(1,5) = "0x18"
  a(1,6) = "0x18"
  a(1,7) = "0x18"
  a(1,8) = "0x18"
  a(1,9) = "0x18"
  a(0,10)= "0x7e"
  a(2,1) = "0x3c" '数字2
  a(2,2) = "0x66"
  a(2,3) = "0x60"
  a(2,4) = "0x60"
  a(2,5) = "0x30"
  a(2,6) = "0x18"
  a(2,7) = "0x0c"
  a(2,8) = "0x06"
  a(2,9) = "0x06"
  a(2,10)= "0x7e"
  a(3,1) = "0x3c" '数字3
  a(3,2) = "0x66"
  a(3,3) = "0xc0"
  a(3,4) = "0x60"
  a(3,5) = "0x1c"
  a(3,6) = "0x60"
  a(3,7) = "0xc0"
  a(3,8) = "0xc0"
  a(3,9) = "0x66"
  a(3,10)= "0x38"
  a(4,1) = "0x38" '数字4
  a(4,2) = "0x3c"
  a(4,3) = "0x36"
  a(4,4) = "0x33"
  a(4,5) = "0x33"
  a(4,6) = "0x33"
  a(4,7) = "0xff"
  a(4,8) = "0x30"
  a(4,9) = "0x30"
  a(4,10)= "0xfe"
  a(5,1) = "0xfe" '数字5
  a(5,2) = "0xfe"
  a(5,3) = "0x06"
  a(5,4) = "0x06"
  a(5,5) = "0x3e"
  a(5,6) = "0x60"
  a(5,7) = "0xc0"
  a(5,8) = "0xc3"
  a(5,9) = "0x66"
  a(5,10)= "0x3c"
  a(6,1) = "0x60" '数字6
  a(6,2) = "0x30"
  a(6,3) = "0x18"
  a(6,4) = "0x0c"
  a(6,5) = "0x3e"
  a(6,6) = "0x63"
  a(6,7) = "0xc3"
  a(6,8) = "0xc3"
  a(6,9) = "0x66"
  a(6,10) ="0x3c"
  a(7,1) = "0xff" '数字7
  a(7,2) = "0xc0"
  a(7,3) = "0x60"
  a(7,4) = "0x30"
  a(7,5) = "0x18"
  a(7,6) = "0x18"
  a(7,7) = "0x18"
  a(7,8) = "0x18"
  a(7,9) = "0x18"
  a(7,10)= "0x18"
  a(8,1) = "0x3c" '数字8
  a(8,2) = "0x66"
  a(8,3) = "0xc3"
  a(8,4) = "0x66"
  a(8,5) = "0x3c"
  a(8,6) = "0x66"
  a(8,7) = "0xc3"
  a(8,8) = "0xc3"
  a(8,9) = "0x66"
  a(8,10)= "0x3c"
  a(9,1) = "0x3c" '数字9
  a(9,2) = "0x66"
  a(9,3) = "0xc3"
  a(9,4) = "0xc3"
  a(9,5) = "0x66"
  a(9,6) = "0x3c"
  a(9,7) = "0x18"
  a(9,8) = "0x0c"
  a(9,9) = "0x06"
  a(9,10)= "0x03"
%>