var re = /src=\"([^\"]*?)\"/i;

  var arr = str.match(re);

  if (arr != undefined && arr.length > 0) {

              insertHtml = arr[1];

  }

         /// <summary>

         /// 获取字符串中img的url集合

         /// </summary>

         /// <param name="content">字符串</param>

         /// <returns></returns>

         public static List<string> getImgUrl(string content)

         {

             Regex rg = new Regex("src=\"([^\"]+)\"", RegexOptions.IgnoreCase);

             var m = rg.Match(content);

             List<string> imgUrl = new List<string>();

             while (m.Success)

             {

                 imgUrl.Add(m.Groups[].Value); //这里就是图片路径

                 m = m.NextMatch();

             }

             return imgUrl;

         }