https://www.cnblogs.com/peasana/p/5242420.html

匯出網路圖片，需要將網路圖片下載到本地或者記憶體流中，建議下載的時候使用縮圖；

高清圖片效率慢；

        Uri uri = new Uri(imgPath); //imgPath :網路圖片地址

        WebRequest webRequest = WebRequest.Create(uri);

        using (WebResponse webResponse = webRequest.GetResponse())

        {

            Bitmap bitmap = new Bitmap(webResponse.GetResponseStream());

            using (MemoryStream ms = new MemoryStream())

            {

                bitmap.Save(ms, System.Drawing.Imaging.ImageFormat.Jpeg);

                byte[] bytes = ms.ToArray();

                int pictureIdx = workbook.AddPicture(bytes, NPOI.SS.UserModel.PictureType.PNG);  //新增圖片

                HSSFPatriarch patriarch = (HSSFPatriarch)sheet.CreateDrawingPatriarch();

                HSSFClientAnchor anchor = new HSSFClientAnchor(0, 0, 0, 240, col, row, col + 1, row + 1);

                //圖片位置，圖片左上角為（col, row）

                HSSFPicture pict = (HSSFPicture)patriarch.CreatePicture(anchor, pictureIdx);

                pict.Resize(); //用圖片原始大小來顯示

            }

        }