string  str = "<form id=\"form1\" runat=\"server\"><div><p><img src=\"img/01300000278409123123126754611.jpg\" alt=\"\" /></p><p><img src=\"img/16583711.jpg\" alt=\"\" /></p><p><img src=\"img/2_091208000854_6.jpg\" alt=\"\" /></p></div></form>";
for (int j = 0; j < GetHtmlImageUrlList(str).Length; j++)
                        {
                             //获取图片路径字符串
                             string img = GetHtmlImageUrlList(str)[i];
                             //删除服务器上的图片
                             string filepath = Server.MapPath(img);
                             FileInfo file = new FileInfo(filepath);
                             if (file.Exists)
                             {
                                 file.Delete();
                             }
                        }

/// <summary>
        /// 获取Img的路径
        /// </summary>
        /// <param name="htmlText">Html字符串文本</param>
        /// <returns>以数组形式返回图片路径</returns>
        public static string[] GetHtmlImageUrlList(string htmlText)
        {
            Regex regImg = new Regex(@"<img\b[^<>]*?\bsrc[\s\t\r\n]*=[\s\t\r\n]*[""']?[\s\t\r\n]*(?<imgUrl>[^\s\t\r\n""'<>]*)[^<>]*?/?[\s\t\r\n]*>", RegexOptions.IgnoreCase);
            //新建一个matches的MatchCollection对象 保存 匹配对象个数(img标签)
            MatchCollection matches = regImg.Matches(htmlText);
            int i = 0;
            string[] sUrlList = new string[matches.Count];
            //遍历所有的img标签对象
            foreach (Match match in matches)
            {
                //获取所有Img的路径src,并保存到数组中
                sUrlList[i++] = match.Groups["imgUrl"].Value;
            }
            return sUrlList;
        }