' PNG Header data
Private Type PNGHeader
    Width As Integer
    Height As Integer
End Type

Private Function GetPNGSize(ByVal filename As String) As PNGHeader
Dim Buffer() As Byte
Dim ChunkSize As Long
Dim ChunkType As String
Dim f As Long

    f = FreeFile()
    Open filename For Binary As #f
        If Err <> 0 Then Exit Function
        If LOF(f) = 0 Then Exit Function
   
        ' Read the first 2 bytes to identifier
        ReDim Buffer(0 To 1)
        Get #f, , Buffer
   
        ' Get the next 6 bytes to confirms that a PNG
        ReDim Buffer(0 To 5)
        Get #f, , Buffer
        If Buffer(0) <> &H4E Or Buffer(1) <> &H47 Or Buffer(2) <> &HD Or _
           Buffer(3) <> &HA Or Buffer(4) <> &H1A Or Buffer(5) <> &HA Then
            Exit Function
        End If
       
        ' Dim the array. Both the chunk size and chunk type have 4 bytes
        ReDim Buffer(0 To 3)
       
        Do While True
            ' Get the chunk size
            Get #f, , Buffer
            ChunkSize = (Buffer(0) * (2 ^ 24)) + (Buffer(1) * (2 ^ 16)) + (Buffer(2) * (2 ^ 8)) + Buffer(3)
           
            ' Get the chunk type
            Get #f, , Buffer
            ChunkType = Chr(Buffer(0)) & Chr(Buffer(1)) & Chr(Buffer(2)) & Chr(Buffer(3))
           
            ' Set the array to chunk size all chunk
            ReDim Buffer(0 To ChunkSize - 1)
            Get #f, , Buffer
           
            Select Case ChunkType
                Case "IHDR"
                    ' Main Chunk with Height, Width
                    GetPNGSize.Width = (Buffer(0) * (2 ^ 24)) + (Buffer(1) * (2 ^ 16)) + (Buffer(2) * (2 ^ 8)) + Buffer(3)
                    GetPNGSize.Height = (Buffer(4) * (2 ^ 24)) + (Buffer(5) * (2 ^ 16)) + (Buffer(6) * (2 ^ 8)) + Buffer(7)
                   
                Case "IDAT", "IEND"
                    Exit Do
            End Select
       
            ReDim Buffer(0 To 3)
           
            ' Jump 4 bytes
            Get #f, , Buffer
        Loop
    Close #f
   
End Function