EPPlus AddPicture为文件中的图像呈现黑盒子

Question

我使用此代码将URL中的图像插入到Excel文件中，但它在文件中呈现为黑框。

string url = Regex.Match(row[column.ColumnName].ToString(), "<img.+?src=[\"'](.+?)[\"'].*?>", RegexOptions.IgnoreCase).Groups[1].Value;
var pic = worksheet.Drawings.AddPicture(Guid.NewGuid().ToString(), ImageUtilities.GetImageFromUrl(url, Request));
pic.SetSize(400,200);
pic.SetPosition(rowIndex, 0, columnIndex, 0);

我已验证从服务器返回的图像是否有效（我已将其保存到文件系统并打开它）以下是获取图像的代码。

 public static Image GetImageFromUrl(string url, HttpRequestBase request) {
            HttpWebRequest httpWebRequest = (HttpWebRequest)HttpWebRequest.Create(url);

            if (request != null) {
                httpWebRequest.CookieContainer = new CookieContainer();
                // add auth cookie and session cookie so graphs/etc will render correctly
                if (request.Cookies[FormsAuthentication.FormsCookieName] != null) {
                    var oldCookie = request.Cookies[FormsAuthentication.FormsCookieName];
                    var cookie = new Cookie(oldCookie.Name,oldCookie.Value, oldCookie.Path,"localhost");
                    httpWebRequest.CookieContainer.Add(cookie);
                }

                if (request.Cookies[PROVIDERPORTALSESSION_COOKIE] != null) {
                    var oldCookie = request.Cookies[PROVIDERPORTALSESSION_COOKIE];
                    var cookie = new Cookie(oldCookie.Name, oldCookie.Value, oldCookie.Path, "localhost");
                    httpWebRequest.CookieContainer.Add(cookie);
                }
            }

            using (HttpWebResponse httpWebReponse = (HttpWebResponse)httpWebRequest.GetResponse()) {
                using (Stream stream = httpWebReponse.GetResponseStream()) {
                    var image= Image.FromStream(stream);
                    return image;
                }
            }
        }