procedure TmyForm.Button1Click(Sender: TObject);
    var mybmp:TBitmap;
begin
    mybmp:= TBitmap.Create();
    try
        mybmp.Assign(Image1.Picture.Bitmap);

        Image1.Picture.Bitmap.SetSize(Image1.Width,Image1.Height);
        Image1.Canvas.Brush.Bitmap := mybmp;
        Image1.Canvas.FillRect(Image1.BoundsRect);

        mybmp.FreeImage;
    finally
        FreeandNil(mybmp)
    end;
end;