如何获知页面上的图象的实际尺寸?

<html>

<head>
<title>千花飞舞之获知图像尺寸</title>
</head>
<body>
<%
graphic="images/intels.gif"
HW = ReadImg(graphic)
Response.Write graphic & " Dimensions: " & HW(0) & "x" & HW(1)
& "<br>"
response.write "<img src=""/" & graphic & """"
response.write height=""" & HW(0) & """
response.write width=""" & HW(0) & "">"
%>
</body></html>

graphicdetect.asp
<%
Dim HW

Function AscAt(s, n)
AscAt = Asc(Mid(s, n, 1))
End Function

Function HexAt(s, n)
HexAt = Hex(AscAt(s, n))
End Function

Function isJPG(fichero)
If inStr(uCase(fichero), ".JPG") <> 0 Then
isJPG = true
Else
isJPG = false
End If
End Function

Function isPNG(fichero)
If inStr(uCase(fichero), ".PNG") <> 0 Then
isPNG = true
Else
isPNG = false
End If
End Function

Function isGIF(fichero)
If inStr(uCase(fichero), ".GIF") <> 0 Then
isGIF = true
Else
isGIF = false
End If
End Function

Function isBMP(fichero)
If inStr(uCase(fichero), ".BMP") <> 0 Then
isBMP = true
Else
isBMP = false
End If
End Function

Function isWMF(fichero)
If inStr(uCase(fichero), ".WMF") <> 0 Then
isWMF = true
Else
isWMF = false
End If
End Function

Function isWebImg(f)
If isGIF(f) Or isJPG(f) Or isPNG(f) Or isBMP(f) Or isWMF(f)
Then
isWebImg = true
Else
isWebImg = true
End If
End Function

Function ReadImg(fichero)
If isGIF(fichero) Then
ReadImg = ReadGIF(fichero)
Else
If isJPG(fichero) Then
ReadImg = ReadJPG(fichero)
Else
If isPNG(fichero) Then
ReadImg = ReadPNG(fichero)
Else
If isBMP(fichero) Then
ReadImg = ReadPNG(fichero)
Else
If isWMF(fichero) Then
ReadImg = ReadWMF(fichero)
Else
ReadImg = Array(0,0)
End If
End If
End If
End If
End If
End Function

Function ReadJPG(fichero)
Dim fso, ts, s, HW, nbytes
HW = Array("","")
Set fso = CreateObject("Scripting.FileSystemObject")
Set ts = fso.OpenTextFile(Server.MapPath("/" & fichero), 1)
s = Right(ts.Read(167), 4)
HW(0) = HexToDec(HexAt(s,3) & HexAt(s,4))
HW(1) = HexToDec(HexAt(s,1) & HexAt(s,2))
ts.Close
ReadJPG = HW
End Function

Function ReadPNG(fichero)
Dim fso, ts, s, HW, nbytes
HW = Array("","")
Set fso = CreateObject("Scripting.FileSystemObject")
Set ts = fso.OpenTextFile(Server.MapPath("/" & fichero), 1)
s = Right(ts.Read(24), 8)
HW(0) = HexToDec(HexAt(s,3) & HexAt(s,4))
HW(1) = HexToDec(HexAt(s,7) & HexAt(s,8))
ts.Close
ReadPNG = HW
End Function

Function ReadGIF(fichero)
Dim fso, ts, s, HW, nbytes
HW = Array("","")
Set fso = CreateObject("Scripting.FileSystemObject")
Set ts = fso.OpenTextFile(Server.MapPath("/" & fichero), 1)
s = Right(ts.Read(10), 4)
HW(0) = HexToDec(HexAt(s,2) & HexAt(s,1))
HW(1) = HexToDec(HexAt(s,4) & HexAt(s,3))
ts.Close
ReadGIF = HW
End Function

Function ReadWMF(fichero)
Dim fso, ts, s, HW, nbytes
HW = Array("","")
Set fso = CreateObject("Scripting.FileSystemObject")
Set ts = fso.OpenTextFile(Server.MapPath("/" & fichero), 1)
s = Right(ts.Read(14), 4)
HW(0) = HexToDec(HexAt(s,2) & HexAt(s,1))
HW(1) = HexToDec(HexAt(s,4) & HexAt(s,3))
ts.Close
ReadWMF = HW
End Function

Function ReadBMP(fichero)
Dim fso, ts, s, HW, nbytes
HW = Array("","")
Set fso = CreateObject("Scripting.FileSystemObject")
Set ts = fso.OpenTextFile(Server.MapPath("/" & fichero), 1)
s = Right(ts.Read(24), 8)
HW(0) = HexToDec(HexAt(s,4) & HexAt(s,3))
HW(1) = HexToDec(HexAt(s,8) & HexAt(s,7))
ts.Close
ReadBMP = HW
End Function

Function isDigit(c)
If inStr("0123456789", c) <> 0 Then
isDigit = true
Else
isDigit = false
End If
End Function

Function isHex(c)
If inStr("0123456789ABCDEFabcdef", c) <> 0 Then
isHex = true
Else
ishex = false
End If
End Function

Function HexToDec(cadhex)
Dim n, i, ch, decimal
decimal = 0
n = Len(cadhex)
For i=1 To n
ch = Mid(cadhex, i, 1)
If isHex(ch) Then
decimal = decimal * 16
If isDigit(c) Then
decimal = decimal + ch
Else
decimal = decimal + Asc(uCase(ch)) - Asc("A")
End If
Else
HexToDec = -1
End If
Next
HexToDec = decimal
End Function
%>

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如何获知页面上的图象的实际尺寸?