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;