获取图片格式的函数GetImageFormat Delphi

function GetImageFormat(AFileName: string): TImageFormat;
var
  aStream: TMemoryStream;
  formatFlag: Word;
begin
  aStream := TMemoryStream.Create;
  try
    aStream.LoadFromFile(AFileName);
    aStream.Position := 0;
    Result := ifUnKnown;
    if aStream.Size = 0 then Exit;

    aStream.ReadBuffer(formatFlag, 2);
    case formatFlag of
      $4D42: Result := ifBmp;
      $D8FF: Result := ifJpg;
      $4947: Result := ifGif;
      $050A: Result := ifPcx;
      $5089: Result := ifPng;
      $4238: Result := ifPsd;
    end;
  finally
    aStream.Free;
  end;
end;