asp.net點擊按鈕下載圖片而不是打開圖片

//下載圖片
Response.ContentType = "application/x-msdownload";
string filename = "attachment; filename=" + "123.jpg";
Response.AddHeader("Content-Disposition", filename);
string filepath = "/images/123.jpg";
Response.TransmitFile(Server.MapPath(filepath));