Как можно прочитать разрешение JPEG-картинки (программирование на Delphi-7)

procedure GetResJpg(JPGFile: string);
const
BufferSize = 50;
var
Buffer: string;
Index: integer;
FileStream: TFileStream;
HorzRes, VertRes: Word;
DP: Byte;
Measure: string;
begin
FileStream := TFileStream.Create(JPGFile,
fmOpenReadWrite);
try
SetLength(Buffer, BufferSize);
FileStream.Read(buffer[1], BufferSize);
Index := Pos('JFIF' + #0$00,buffer);
if Index > 0 then
begin
FileStream.Seek(Index + 6, soFromBeginning);
FileStream.Read(DP, 1);
case DP of
1: Measure := 'DPI'; //Dots Per Inch
2: Measure := 'DPC'; //Dots Per Cm.
end;
FileStream.Read(HorzRes, 2); // x axis
HorzRes := Swap(HorzRes);
FileStream.Read(VertRes, 2); // y axis
VertRes := Swap(VertRes);
end
finally
FileStream.Free;
end;
end;