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procedure TForm1.Button1Click(Sender: TObject);
var
  OldBkMode: integer;
begin
  Image1.Picture.Bitmap.Canvas.Font.Color := clBlue;
  OldBkMode := SetBkMode(Image1.Picture.Bitmap.Canvas.Handle, TRANSPARENT);
  Image1.Picture.Bitmap.Canvas.TextOut(10, 10, 'Hello');
  SetBkMode(Image1.Picture.Bitmap.Canvas.Handle, OldBkMode);
end;