static void Main(string[] args)
        {
            List<string> list = new List<string>()
            {
                "http://bbs.unpcn.com/attachment.aspx?attachmentid=3827974",
                "http://b.hiphotos.baidu.com/image/pic/item/f603918fa0ec08fa587802075aee3d6d55fbda11.jpg"
            };

            foreach (var item in list)
            {
                WebClient w = new WebClient();
                Uri u = new Uri(item);
                w.DownloadFileAsync(u,System.Guid.NewGuid().ToString("N")+".jpg");
            }
        }