procedure TForm1.Button1Click(Sender: TObject);
var
aBitmap: TBitmap;
aRectF: TRectF;
begin
aBitmap := TBitmap.Create;
aBitmap.SetSize(trunc(Image1.Width), trunc(Image1.Height));
aBitmap.Assign(Image1.Bitmap);
aBitmap.Canvas.BeginScene;
aRectF := RectF(aBitmap.Width - 100, aBitmap.Height - 25, aBitmap.Width, aBitmap.Height);
aBitmap.Canvas.Fill.Color := $B4FFFFE5;
aBitmap.Canvas.FillRect(aRectF, 0, 0, AllCorners, 1);
aBitmap.Canvas.Font.Size := 18;
aBitmap.Canvas.Fill.Color := TAlphaColorRec.Black;
aBitmap.Canvas.FillText(aRectF, DateToStr(Date), false, 1, [], TTextAlign.Center, TTextAlign.Center);
aBitmap.Canvas.EndScene;
Image1.Bitmap.Assign(aBitmap);
aBitmap.Free;
end;