BMP圖片規則：BMP文件有54個字節的文件頭，其中包括了BMP文件標誌“BM”，文件大小，位圖文件起始位置，長，寬，位圖位數1/4/8/24（1,8個像素占1個字節;4，2個像素占1個字節;8，1個像素占1個字節;24,1個像素占3個字節;）等信息。不過最簡單的方法是先用畫圖板做一個相同大小的空圖片，把頭信息記錄下來。
BMP文件實際顯示部分，是從左下角開始，到右上角結束，詳細記錄了文件的每個像素，如果用24位位圖表示的話，用3個字節表示RGB。紅色表示就是 ff 00 ff，黑色就是00 00 00，白色是ff ff ff...
如果我們要表示一個數字或字母，我們可以用一個10X10的距陣來表示，比如1用下麵的距陣表示：
1111011111
1100011111
1111011111
1111011111
1111011111
1111011111
1111011111
1111011111
1111011111
1100000111
當然也可以用一個更大的距陣來表示一個更豐富的樣式。
明白了原理，接下來就好用程序實現了，我們用Response.BinaryWrite方法寫入文件頭，再用程序寫入文件體。
下麵是一個用程序生成瀏覽者IP地址的程序：
<%
Response.Expires = -9999
Response.AddHeader "cache-control","no-cache"
Response.ContentType = "Image/BMP"
Const cCode = "0123456789. " '數據值
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) '劈開IP
for j=0 to 3 '處理分組
if len(ls(j))<3 then '如果長度少於3
spac=""
for k=1 to 3-len(ls(j)) '加3-len個空格
spac=spac+" "
next
ls(j)=spac+ls(j) '轉換長度足夠的ls(j)
end if
next
str="" '二次處理IP串,over
for k=0 to 3
str=str+ls(k)+"."
next
str=left(str,15)
dim vCode(15) '三次處理成數組
For x = 0 To 14
vCode(x) = mid(str,x+1,1) '等於什麼值?
vCode(x)=instr(1,cCode,vCode(x),1)-1 '值在串中是第幾?
'response.write vCode(x)&"<br>"
Next
Dim vNumber(12)
vNumber(0) = "111000011111011110111101
vNumber(1) = "111101111111000111111111
vNumber(2) = "111000011111011110111101
vNumber(3) = "111000011111011110111101
vNumber(4) = "111110111111111011111111
vNumber(5) = "110000001111011111111101
vNumber(6) = "111100011111101110111101
vNumber(7) = "110000001111011101111101
vNumber(8) = "111000011111011110111101
vNumber(9) = "111000111111011101111101
vNumber(10) ="111111111111111111111111
vNumber(11) ="111111111111111111111111
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，因為vColor()已經定義每個RGB值了，如果是8位位圖，使用一個字節即可
Response.BinaryWrite vColor(Mid(vNumber(vCode(y)), x * 10 + z , 1)) '寫入流
Next
Next
Response.BinaryWrite vColor(1) '為每一行的增加一個行尾標誌
Next
%>
當然，這個程序生成的流和位圖定義有點不太符合，圖片有點斜，大家慢慢研究吧...
下麵是我修改的網上的生成彩色隨機驗證碼的程序, 附件一直提示file1格式不對, 隻好粘在下麵
<%
Response.ContentType = "Image/BMP"
Call Com_CreatValidCode()
Sub Com_CreatValidCode()
Randomize
Dim i, ii, iii
Const cAmount = 36 '數值個數
Const cCode = "0123456789ABCDEFGHIJKLMN
Dim vColorData(2)
vColorData(0) = "" '黑色點要轉為彩色點,暫時不定義
vColorData(1) = ChrB(255) & ChrB(255) & ChrB(255) '白點
Dim vCode(4), vCodes '產生一組任意數
For i = 0 To 3
vCode(i) = Int(Rnd * cAmount) '數組等於總數*隨機數
vCodes=vCodes&Mid(cCode,vCode(i)+1,1) '串等於串加上後續值
Next
session("checkcode")=vCodes '記錄產生的串值
Dim vNumberData(36)
vNumberData(0) = "111000011111011110111101
vNumberData(1) = "111101111111000111111111
vNumberData(2) = "111000011111011110111101
vNumberData(3) = "111000011111011110111101
vNumberData(4) = "111110111111111011111111
vNumberData(5) = "110000001111011111111101
vNumberData(6) = "111100011111101110111101
vNumberData(7) = "110000001111011101111101
vNumberData(8) = "111000011111011110111101
vNumberData(9) = "111000111111011101111101
vNumberData(10) = "111101111111110111111110
vNumberData(11) = "100000011111011110111101
vNumberData(12) = "111000001111011110111011
vNumberData(13) = "100000111111011101111101
vNumberData(14) = "100000011111011110111101
vNumberData(15) = "100000011111011110111101
vNumberData(16) = "111000011111011101111011
vNumberData(17) = "100010001111011101111101
vNumberData(18) = "110000011111110111111111
vNumberData(19) = "111000001111111011111111
vNumberData(20) = "100010001111011101111101
vNumberData(21) = "100011111111011111111101
vNumberData(22) = "100010001111001001111100
vNumberData(23) = "100010001111001101111100
vNumberData(24) = "111000111111011101111011
vNumberData(25) = "100000011111011110111101
vNumberData(26) = "111000111111011101111011
vNumberData(27) = "100000111111011101111101
vNumberData(28) = "111000001111011110111101
vNumberData(29) = "100000001110110110111111
vNumberData(30) = "100010001111011101111101
vNumberData(31) = "100010001111011101111101
vNumberData(32) = "100101001111010101111101
vNumberData(33) = "100010001111011101111110
vNumberData(34) = "100010001111011101111101
vNumberData(35) = "110000001111011101111111
Response.BinaryWrite ChrB(66) & ChrB(77) & ChrB(230) & ChrB(4) & 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(40) & ChrB(0) & ChrB(0) & ChrB(0) & ChrB(10) & ChrB(0) &_
ChrB(0) & ChrB(0) & ChrB(1) & ChrB(0)
Response.BinaryWrite ChrB(24) & ChrB(0) & ChrB(0) & ChrB(0) & ChrB(0) & ChrB(0) & ChrB(176) & ChrB(4) &_
ChrB(0) & ChrB(0) & ChrB(18) & ChrB(11) & ChrB(0) & ChrB(0) & ChrB(18) & ChrB(11) &_
ChrB(0) & ChrB(0) & ChrB(0) & ChrB(0) & ChrB(0) & ChrB(0) & ChrB(0) & ChrB(0) &_
ChrB(0) & ChrB(0)
For i = 9 To 0 Step -1 '行
For ii = 0 To 3 '字數
For iii = 1 To 10 '像素點
if Mid(vNumberData(vCode(ii)), i * 10 + iii , 1) ="0" then '產生彩色點,減去一個固定值,可使顏色偏深
dim a,b,c
a=abs(Rnd * 256-60)
b=abs(Rnd * 256-128)
c=abs(Rnd * 256-60)
vColorData(0) = ChrB(a) & ChrB(b) & ChrB(c)
Response.BinaryWrite vColorData(Mid(vNumberData(vCode(ii)), i * 10 + iii , 1))
else
dim d,e,f '產生彩色背景，顏色偏淺，也可以隨機生成噪點做背景
d=abs(Rnd * 255)
e=abs(Rnd * 255)
f=abs(Rnd * 255)
if d+e+f>580 then
vColorData(1) = ChrB(d) & ChrB(e) & ChrB(f)
Response.BinaryWrite vColorData(Mid(vNumberData(vCode(ii)), i * 10 + iii , 1))
else
Response.BinaryWrite vColorData(Mid(vNumberData(vCode(ii)), i * 10 + iii , 1))
end if
end if
Next
Next
Next
End Sub
%>
------------------------------------------------------------------------------
另做的一個小IP圖片
--------------------------------------------------------------------------------
黑白8位位圖圖片,非常正規,圖片非常小:262個字節
注:8位黑白位圖,指8個像素占一個字節,第一個點是黑色,另七個點是白色的話,字節值是80;第二點是黑色,其它點是白色,字節值是40,以此類推...多個點是黑色加在一起,8個像素全是黑色,字節值是FF...
<%
Response.Expires = -9999
Response.AddHeader "cache-control","no-cache"
Response.ContentType = "Image/BMP"
Const cCode = "0123456789. " '數據值
Dim vColor(2)
vColor(0) = ChrB(0) '黑
vColor(1) = ChrB(80) '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) '劈開IP
for j=0 to 3 '處理分組
if len(ls(j))<3 then '如果長度少於3
spac=""
for k=1 to 3-len(ls(j)) '加3-len個空格
spac=spac+" "
next
ls(j)=spac+ls(j) '轉換長度足夠的ls(j)
end if
next
str="" '二次處理IP串
for k=0 to 3
str=str+ls(k)+"."
next
str=left(str,15)
Dim vNumber(12)
vNumber(0) = "111000011111011110111101
vNumber(1) = "111101111111000111111111
vNumber(2) = "111000011111011110111101
vNumber(3) = "111000011111011110111101
vNumber(4) = "111110111111111011111111
vNumber(5) = "110000001111011111111101
vNumber(6) = "111100011111101110111101
vNumber(7) = "110000001111011101111101
vNumber(8) = "111000011111011110111101
vNumber(9) = "111000111111011101111101
vNumber(10) ="111111111111111111111111
vNumber(11) ="111111111111111111111111
dim x,y,vCode(15) '三次處理成數組
For x = 0 To 14
vCode(x) = mid(str,x+1,1) '等於什麼值?
vCode(x)=instr(1,cCode,vCode(x),1)-1 '值在串中是第幾?
Next
Response.BinaryWrite chrB(66)&chrB(77)&chrB(8)&chrB(1)&chrB(0)&chrB(0)&chrB(0)&chrB(0)&chrB(0)&chrB(0)&chrB(62)&_
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(1)&chrB(0)&chrB(0)&chrB(0)&chrB(0)&chrB(0)&chrB(202)
Response.BinaryWrite chrB(0)&chrB(0)&chrB(0)&chrB(18)&chrB(11)&chrB(0)&chrB(0)&chrB(18)&chrB(11)&chrB(0)&chrB(0)&_
chrB(0)&chrB(0)&chrB(0)&chrB(0)&chrB(0)&chrB(0)&chrB(0)&chrB(0)&chrB(255)&chrB(255)&chrB(255)&chrB(0)&chrB(0)&_
chrB(0)&chrB(0)&chrB(0)
dim points(10)
for x=9 to 0 step -1 '處理成10行150列的像素串
points(x)=""
for y=0 to 14
points(x)=points(x)&mid(vNumber(vCode(y)),x*10+1,10)
next
for z=0 to 18 '劈開像素串，分別處理
lsstr=mid(points(x),z*8+1,8)
byteval=0
if mid(lsstr,1,1)="0" then byteval=byteval+128
if mid(lsstr,2,1)="0" then byteval=byteval+64
if mid(lsstr,3,1)="0" then byteval=byteval+32
if mid(lsstr,4,1)="0" then byteval=byteval+16
if mid(lsstr,5,1)="0" then byteval=byteval+8
if mid(lsstr,6,1)="0" then byteval=byteval+4
if mid(lsstr,7,1)="0" then byteval=byteval+2
if mid(lsstr,8,1)="0" then byteval=byteval+1
response.binarywrite chrb(byteval)
next
Response.BinaryWrite vColor(0) '寫行尾標誌
next
Response.BinaryWrite vColor(0) '寫圖尾標誌
%>
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