查找文本中IMG标签 替换SRC属性值

private static string Contentformat(string strText)
    {
        //处理后的结果。
        StringBuilder sbNewText = new StringBuilder();


        //找到所有图片，替换Src
        //Regex regImg = new Regex(@"<(img|embed|bgsound|object)[^<>]*>", RegexOptions.IgnoreCase);
        //MatchCollection matchs = regImg.Matches(strText);
        strText = strText.Replace("<", "<");
        strText = strText.Replace(">", ">");
        Regex regImg = new Regex(@"]*?\bsrc[\s\t\r\n]*=[\s\t\r\n]*[""']?[\s\t\r\n]*(?[^\s\t\r\n""'<>]*)[^<>]*?/?[\s\t\r\n]*>", RegexOptions.IgnoreCase);
        MatchCollection matchs = regImg.Matches(strText);
        if (matchs.Count == 0)
        {
            return strText;
        }
        else
        {
            int curPos = 0;
            foreach (Match m in matchs)
            {
                sbNewText.Append(strText.Substring(curPos, m.Index - curPos));
                curPos = m.Index + m.Length;
                string imgTag = m.Value;
                string url = System.Web.HttpContext.Current.Server.MapPath("~/FileSystem/41/") + m.Groups["imgUrl"].Value;
                string base64Img = Convert.ToBase64String(System.IO.File.ReadAllBytes(url));
                string img = "";
                //string img = "";
                sbNewText.Append("
");
                sbNewText.Append(img);
            }
        }
        return sbNewText.ToString();
    }