返回第一个<img...>标签

public string GetImgUrl(string HTMLStr)
    {
        string str = string.Empty;
        //string sPattern = @"^<img\s+[^>]*>";
        Regex r = new Regex(@"<img\s+[^>]*\s*src\s*=\s*([']?)(?<url>\S+)'?[^>]*>",
        RegexOptions.Compiled);
        Match m = r.Match(HTMLStr.ToLower());
        if (m.Success)
            str = m.Result("${url}");
        return str;
    }