BMP图片规则：BMP文件有54个字节的文件头，其中包括了BMP文件标志“BM”，文件大小，位图文件起始位置，长，宽，位图位数1/4/8/24（1,8个像素占1个字节;4，2个像素占1个字节;8，1个像素占1个字节;24,1个像素占3个字节;）等信息。不过最简单的方法是先用画图板做一个相同大小的空图片，把头信息记录下来。
BMP文件实际显示部分，是从左下角开始，到右上角结束，详细记录了文件的每个像素，如果用24位位图表示的话，用3个字节表示RGB。红色表示就是 ff 00 ff，黑色就是00 00 00，白色是ff ff ff...
如果我们要表示一个数字或字母，我们可以用一个10X10的距阵来表示，比如1用下面的距阵表示：
1111011111
1100011111
1111011111
1111011111
1111011111
1111011111
1111011111
1111011111
1111011111
1100000111
当然也可以用一个更大的距阵来表示一个更丰富的样式。
明白了原理，接下来就好用程序实现了，我们用Response.BinaryWrite方法写入文件头，再用程序写入文件体。
下面是一个用程序生成浏览者IP地址的程序：
<%
Response.Expires = -9999
Response.AddHeader "cache-control","no-cache"
Response.ContentType = "Image/BMP"
Const cCode = "0123456789. " '数据值
Dim vColor(2)
vColor(0) = ChrB(0) & ChrB(0) & ChrB(0) '黑
vColor(1) = ChrB(255) & ChrB(255) & ChrB(255) '白
ip=request.ServerVariables("http_x_forwarded_for") '得到IP值
if ip="" then
ip=request.ServerVariables("remote_addr")
end if
ls=split(ip,".",-1,1) '劈开IP
for j=0 to 3 '处理分组
if len(ls(j))<3 then '如果长度少于3
spac=""
for k=1 to 3-len(ls(j)) '加3-len个空格
spac=spac+" "
next
ls(j)=spac+ls(j) '转换长度足够的ls(j)
end if
next
str="" '二次处理IP串,over
for k=0 to 3
str=str+ls(k)+"."
next
str=left(str,15)
dim vCode(15) '三次处理成数组
For x = 0 To 14
vCode(x) = mid(str,x+1,1) '等于什么值?
vCode(x)=instr(1,cCode,vCode(x),1)-1 '值在串中是第几?
'response.write vCode(x)&"
"
Next
Dim vNumber(12)
vNumber(0) = "1110000111110111101111011110111101001011110100101111010010111101001011110111101111011110111110000111"
vNumber(1) = "1111011111110001111111110111111111011111111101111111110111111111011111111101111111110111111100000111"
vNumber(2) = "1110000111110111101111011110111111111011111111011111111011111111011111111011111111011110111100000011"
vNumber(3) = "1110000111110111101111011110111111110111111100111111111101111111111011110111101111011110111110000111"
vNumber(4) = "1111101111111110111111110011111110101111110110111111011011111100000011111110111111111011111111000011"
vNumber(5) = "1100000011110111111111011111111101000111110011101111111110111111111011110111101111011110111110000111"
vNumber(6) = "1111000111111011101111011111111101111111110100011111001110111101111011110111101111011110111110000111"
vNumber(7) = "1100000011110111011111011101111111101111111110111111110111111111011111111101111111110111111111011111"
vNumber(8) = "1110000111110111101111011110111101111011111000011111101101111101111011110111101111011110111110000111"
vNumber(9) = "1110001111110111011111011110111101111011110111001111100010111111111011111111101111011101111110001111"
vNumber(10) ="1111111111111111111111111111111111111111111111111111111111111111111111111111111111110011111111001111"
vNumber(11) ="1111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111"
Response.BinaryWrite chrB(66)&chrB(77)&chrB(222)&chrB(17)&chrB(0)&chrB(0)&chrB(0)&chrB(0)&chrB(0)&chrB(0)&chrB(54)&_
chrB(0)&chrB(0)&chrB(0)&chrB(40)&chrB(0)&chrB(0)&chrB(0)&chrB(150)&chrB(0)&chrB(0)&chrB(0)&chrB(10)&chrB(0)&chrB(0)&_
chrB(0)&chrB(1)&chrB(0)&chrB(24)&chrB(0)&chrB(0)&chrB(0)&chrB(0)&chrB(0)&chrB(168)&chrB(17)
Response.BinaryWrite chrB(0)&chrB(0)&chrB(0)&chrB(0)&chrB(0)&chrB(0)&chrB(0)&chrB(0)&chrB(0)&chrB(0)&chrB(0)&chrB(0)&_
chrB(0)&chrB(0)&chrB(0)&chrB(0)&chrB(0)&chrB(0)
dim x,y,z
For x = 9 To 0 step -1 '逐行
For y = 0 To 14 '逐字
For z = 1 To 10 '逐像素的R/G/B，因为vColor()已经定义每个RGB值了，如果是8位位图，使用一个字节即可
Response.BinaryWrite vColor(Mid(vNumber(vCode(y)), x * 10 + z , 1)) '写入流
Next
Next
Response.BinaryWrite vColor(1) '为每一行的增加一个行尾标志
Next
%>
当然，这个程序生成的流和位图定义有点不太符合，图片有点斜，大家慢慢研究吧...
下面是我修改的网上的生成彩色随机验证码的程序, 附件一直提示file1格式不对, 只好粘在下面
<%
Response.ContentType = "Image/BMP"
Call Com_CreatValidCode()
Sub Com_CreatValidCode()
Randomize
Dim i, ii, iii
Const cAmount = 36 '数值个数
Const cCode = "0123456789ABCDEFGHIJKLMNOPQRSTUVWXYZ" '数值范围
Dim vColorData(2)
vColorData(0) = "" '黑色点要转为彩色点,暂时不定义
vColorData(1) = ChrB(255) & ChrB(255) & ChrB(255) '白点
Dim vCode(4), vCodes '产生一组任意数
For i = 0 To 3
vCode(i) = Int(Rnd * cAmount) '数组等于总数*随机数
vCodes=vCodes&Mid(cCode,vCode(i)+1,1) '串等于串加上后续值
Next
session("checkcode")=vCodes '记录产生的串值
Dim vNumberData(36)
vNumberData(0) = "1110000111110111101111011110111101001011110100101111010010111101001011110111101111011110111110000111"
vNumberData(1) = "1111011111110001111111110111111111011111111101111111110111111111011111111101111111110111111100000111"
vNumberData(2) = "1110000111110111101111011110111111111011111111011111111011111111011111111011111111011110111100000011"
vNumberData(3) = "1110000111110111101111011110111111110111111100111111111101111111111011110111101111011110111110000111"
vNumberData(4) = "1111101111111110111111110011111110101111110110111111011011111100000011111110111111111011111111000011"
vNumberData(5) = "1100000011110111111111011111111101000111110011101111111110111111111011110111101111011110111110000111"
vNumberData(6) = "1111000111111011101111011111111101111111110100011111001110111101111011110111101111011110111110000111"
vNumberData(7) = "1100000011110111011111011101111111101111111110111111110111111111011111111101111111110111111111011111"
vNumberData(8) = "1110000111110111101111011110111101111011111000011111101101111101111011110111101111011110111110000111"
vNumberData(9) = "1110001111110111011111011110111101111011110111001111100010111111111011111111101111011101111110001111"
vNumberData(10) = "1111011111111101111111101011111110101111111010111111101011111100000111110111011111011101111000100011"
vNumberData(11) = "1000000111110111101111011110111101110111110000111111011101111101111011110111101111011110111000000111"
vNumberData(12) = "1110000011110111101110111110111011111111101111111110111111111011111111101111101111011101111110001111"
vNumberData(13) = "1000001111110111011111011110111101111011110111101111011110111101111011110111101111011101111000001111"
vNumberData(14) = "1000000111110111101111011011111101101111110000111111011011111101101111110111111111011110111000000111"
vNumberData(15) = "1000000111110111101111011011111101101111110000111111011011111101101111110111111111011111111000111111"
vNumberData(16) = "1110000111110111011110111101111011111111101111111110111111111011100011101111011111011101111110001111"
vNumberData(17) = "1000100011110111011111011101111101110111110000011111011101111101110111110111011111011101111000100011"
vNumberData(18) = "1100000111111101111111110111111111011111111101111111110111111111011111111101111111110111111100000111"
vNumberData(19) = "1110000011111110111111111011111111101111111110111111111011111111101111111110111110111011111000011111"
vNumberData(20) = "1000100011110111011111011011111101011111110001111111010111111101101111110110111111011101111000100011"
vNumberData(21) = "1000111111110111111111011111111101111111110111111111011111111101111111110111111111011110111000000011"
vNumberData(22) = "1000100011110010011111001001111100100111110101011111010101111101010111110101011111010101111001010011"
vNumberData(23) = "1000100011110011011111001101111101010111110101011111010101111101100111110110011111011001111000110111"
vNumberData(24) = "1110001111110111011110111110111011111011101111101110111110111011111011101111101111011101111110001111"
vNumberData(25) = "1000000111110111101111011110111101111011110000011111011111111101111111110111111111011111111000111111"
vNumberData(26) = "1110001111110111011110111110111011111011101111101110111110111011111011101001101111011001111110001011"
vNumberData(27) = "1000001111110111011111011101111101110111110000111111010111111101101111110110111111011101111000110011"
vNumberData(28) = "1110000011110111101111011110111101111111111001111111111001111111111011110111101
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