Determine the Width/Height of an Image through ASP

<%
  ':::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::
  ':::                                                             :::
  ':::  This routine will attempt to identify any filespec passed  :::
  ':::  as a graphic file (regardless of the extension). This will :::
  ':::  work with GIF or JPG files.                     	   :::
  ':::                                                             :::
  ':::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::
  ':::          Based on ideas presented by David Crowell          :::
  ':::                   (credit where due)                        :::
  ':::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::
  ':::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::
  ':::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::
  '::: blah blah blah blah blah blah blah blah blah blah blah blah :::
  '::: blah blah blah blah blah blah blah blah blah blah blah blah :::
  '::: blah blah     Copyright *c* MM,  Mike Shaffer     blah blah :::
  '::: blah blah      ALL RIGHTS RESERVED WORLDWIDE      blah blah :::
  '::: blah blah  Permission is granted to use this code blah blah :::
  '::: blah blah   in your projects, as long as this     blah blah :::
  '::: blah blah      copyright notice is included       blah blah :::
  '::: blah blah blah blah blah blah blah blah blah blah blah blah :::
  '::: blah blah blah blah blah blah blah blah blah blah blah blah :::
  ':::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::

  ':::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::
  ':::                                                             :::
  ':::  This function gets a specified number of bytes from any    :::
  ':::  file, starting at the offset (base 1)                      :::
  ':::                                                             :::
  ':::  Passed:                                                    :::
  ':::       sFileName        => Filespec of file to read          :::
  ':::       offset      => Offset at which to start reading       :::
  ':::       bytes       => How many bytes to read                 :::
  ':::                                                             :::
  ':::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::
  function GetBytes(sFileName, offset, bytes)

     Dim objFSO
     Dim objFTemp
     Dim objTextStream
     Dim lngSize

     on error resume next

     Set objFSO = CreateObject("Scripting.FileSystemObject")
     
     ' First, we get the filesize
     Set objFTemp = objFSO.GetFile(sFileName)
     lngSize = objFTemp.Size
     set objFTemp = nothing

     fsoForReading = 1
     Set objTextStream = objFSO.OpenTextFile(sFileName, fsoForReading)

     if offset > 0 then
        strBuff = objTextStream.Read(offset - 1)
     end if

     if bytes = -1 then		' Get All!

        GetBytes = objTextStream.Read(lngSize)  'ReadAll

     else

        GetBytes = objTextStream.Read(bytes)

     end if
    
     objTextStream.Close
     set objTextStream = nothing
     set objFSO = nothing

  end function


  ':::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::
  ':::                                                             :::
  ':::  Functions to convert two bytes to a numeric value (long)   :::
  ':::  (both little-endian and big-endian)                        :::
  ':::                                                             :::
  ':::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::
  function lngConvert(strTemp)
     lngConvert = clng(asc(left(strTemp, 1)) + ((asc(right(strTemp, 1)) * 256)))
  end function

  function lngConvert2(strTemp)
     lngConvert2 = clng(asc(right(strTemp, 1)) + ((asc(left(strTemp, 1)) * 256)))
  end function

  
  ':::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::
  ':::                                                             :::
  ':::  This function does most of the real work. It will attempt  :::
  ':::  to read any file, regardless of the extension, and will    :::
  ':::  identify if it is a graphical image.                       :::
  ':::                                                             :::
  ':::  Passed:                                                    :::
  ':::       sFileName        => Filespec of file to read          :::
  ':::       width       => width of image                         :::
  ':::       height      => height of image                        :::
  ':::                                                             :::
  ':::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::
  function gfxSpex(sFileName, width, height)
  	'get the width and height of the passed file
  	'can only be a GIF or JPG

     dim strGIF
     dim strType
     strType = ""
     strImageType = "(unknown)"

     gfxSpex = False
     
     strGIF = "GIF"

     strType = GetBytes(sFileName, 0, 3)

     if strType = strGIF then				' is GIF

        strImageType = "GIF"
        Width = lngConvert(GetBytes(sFileName, 7, 2))
        Height = lngConvert(GetBytes(sFileName, 9, 2))
        gfxSpex = True

     else

        strBuff = GetBytes(sFileName, 0, -1)		' Get all bytes from file
        lngSize = len(strBuff)
        flgFound = 0

        strTarget = chr(255) & chr(216) & chr(255)
        flgFound = instr(strBuff, strTarget)

        if flgFound = 0 then
           exit function
        end if

        strImageType = "JPG"
        lngPos = flgFound + 2
        ExitLoop = false

        do while ExitLoop = False and lngPos < lngSize

           do while asc(mid(strBuff, lngPos, 1)) = 255 and lngPos < lngSize
              lngPos = lngPos + 1
           loop

           if asc(mid(strBuff, lngPos, 1)) < 192 or asc(mid(strBuff, lngPos, 1)) > 195 then
              lngMarkerSize = lngConvert2(mid(strBuff, lngPos + 1, 2))
              lngPos = lngPos + lngMarkerSize  + 1
           else
              ExitLoop = True
           end if

       loop

       if ExitLoop = False then

          Width = -1
          Height = -1

       else

          Height = lngConvert2(mid(strBuff, lngPos + 4, 2))
          Width = lngConvert2(mid(strBuff, lngPos + 6, 2))
          gfxSpex = True

       end if
                   
     end if

  end function

%>

'get the image path
sPath = "image.gif"

If gfxSpex(Server.Mappath(sPath), w, h) then
	'if a valid image (GIF or JPG) get dimensions
	response.write "Width = " & w
	response.write "<br>Height = " & h
End If