Solution: use TeeChart's own routines:

eg. (uses TeeJPEG, TeExport
TeeSavePanel(TJPEGExportFormat,AChart);

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or
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Fix applicable to application (client test) code:

Backup and restore Chart Canvas.

eg.
procedure TForm1.ExportJPEG(Sender: TObject; AChart : TChart);
var
  FName: string;
  tmpBitmap:TBitmap;
  OldCanvas : TCanvas;
begin
  OldCanvas := AChart.Canvas.ReferenceCanvas;

  with TJPEGImage.Create do begin
    tmpBitmap:=TBitmap.Create;   { <-- create a temporary TBitmap }
    try
      tmpBitmap.Width :=AChart.Width;   { <-- set the bitmap dimensions }
      tmpBitmap.Height:=AChart.Height;
      AChart.Draw(tmpBitmap.Canvas,Rect(0,0,tmpBitmap.Width,tmpBitmap.Height));
      Assign(tmpBitmap);

      SaveToFile('d:\data\output\testjpeg2.jpg'); {<-- save the JPEG to disk }
    finally
      tmpBitmap.Free;  { <-- free the temporary Bitmap }
    end;

    Free;  { <-- free the temporary JPEG object }
  end;

  AChart.Canvas.ReferenceCanvas := OldCanvas;
end;