procedure TMyPersistentObject.LoadBitmapProperty(Reader: TReader);
var
  ms: TMemoryStream;
begin
   ms := TMemoryStream.Create;
   try
      ms.Size := Reader.ReadInt64;
      Reader.Read(ms.Memory^, ms.Size);
      MyBitmapProperty.LoadFromStream(ms);
   finally
     ms.Free;
   end;
end;

procedure TMyPersistentObject.StoreBitmapProperty(Writer: TWriter);
var
  ms: TMemoryStream;
  Size: Int64;
begin
   ms := TMemoryStream.Create;
   try
      MyBitmapProperty.SaveToStream(ms);
      Size := ms.Size;      
      Writer.Write(Size, SizeOf(Size));
      Writer.Write(ms.Memory^, Size);
   finally
     ms.Free;
   end;
end;

procedure TMyPersistentObject.DefineProperties(Filer: TFiler);
begin
 inherited;
 Filer.DefineProperty('MyBitmapProperty', LoadBitmapProperty, StoreBitmapProperty, True);
end;

procedure TBitmap.WriteData(Stream: TStream);
begin
 WriteStream(Stream, True);
end;

procedure TBitmap.ReadData(Stream: TStream);
var Size: Longint;
begin
 Stream.Read(Size, SizeOf(Size));
 ReadStream(Stream, Size);
end;