procedure TForm1.Button2Click(Sender: TObject);
var
bm: TBitmap;
begin
bm := TBitmap.create;
bm.Width := 50; //指明图片的 width
bm.Height := 50; //指明图片的 height
bm.Canvas.CopyRect(rect(0, 0, 50, 50), canvas, rect(0, 0, 50, 50));
//目标区域 想要复制的区域
bm.SaveToFile('f:/fff.bmp');
bm.Free;
end;