Uses JPEG;
...
Function JPEG_to_BMP(jpg:TJPEGImage):TBitMap;
begin
  Result := TBitmap.Create;
  Result.Assign(jpg);
end;

Procedure TForm1.Button1Click(Sender: TObject);
var jpg:TJPEGImage;
    bmp:TBitMap;
begin
  jpg := TJPEGImage.Create;
  bmp := TBitMap.Create;

  jpg.LoadFromFile('d:\1.jpg');

  bmp:=JPEG_to_BMP(jpg);
end;