/// <summary>
 /// 下載指定ＵＲＬ下的所有圖片
 /// </summary>
 public class WebPageImage
 {
 /// <summary>
 /// 獲取網頁中全部圖片
 /// </summary>
 /// <param name="url">網頁地址</param>
 /// <param name="charSet">網頁編碼，為空自動判斷</param>
 /// <returns>全部圖片顯示代碼</returns>
 public string getImages(string url, string charSet)
 {
 string s = getHtml(url, charSet);
 return getPictures(s, url);
 }

 /// <summary>
 /// 獲取網頁中全部圖片
 /// </summary>
 /// <param name="url">網址</param>
 /// <returns>全部圖片代碼</returns>
 public string getImages(string url)
 {
 return getImages(url, "");
 }

 string doman(string url)
 {
 Uri u = new Uri(url);
 return u.Host;
 }

 /// <summary>
 /// 獲取網頁內容
 /// </summary>
 /// <param name="url">網站地址</param>
 /// <param name="charSet">目標網頁的編碼,如果傳入的是null或者"",那就自動分析網頁的編碼 </param>
 /// <returns></returns>
 string getHtml(string url, string charSet)
 {
 WebClient myWebClient = new WebClient();
 //創建WebClient實例myWebClient 
 // 需要注意的： 
 //有的網頁可能下不下來，有種種原因比如需要cookie,編碼問題等等 
 //這是就要具體問題具體分析比如在頭部加入cookie 
 // webclient.Headers.Add("Cookie", cookie); 
 //這樣可能需要一些重載方法。根據需要寫就可以了 

 //獲取或設置用于對向 Internet 資源的請求進行身份驗證的網絡憑據。 
 myWebClient.Credentials = CredentialCache.DefaultCredentials;
 //如果服務器要驗證用戶名,密碼 
 //NetworkCredential mycred = new NetworkCredential(struser, strpassword); 
 //myWebClient.Credentials = mycred; 
 //從資源下載數據并返回字節數組。（加@是因為網址中間有"/"符號） 
 byte[] myDataBuffer = myWebClient.DownloadData(url);
 string strWebData = Encoding.Default.GetString(myDataBuffer);

 //獲取網頁字符編碼描述信息 
 Match charSetMatch = Regex.Match(strWebData, "<meta([^<]*)charset=([^<]*)\"", RegexOptions.IgnoreCase | RegexOptions.Multiline);
 string webCharSet = charSetMatch.Groups[2].Value.Replace("\"", "");
 if (charSet == null || charSet == "")
 charSet = webCharSet;

 if (charSet != null && charSet != "" && Encoding.GetEncoding(charSet) != Encoding.Default)
 strWebData = Encoding.GetEncoding(charSet).GetString(myDataBuffer);
 return strWebData;
 }

 string getPictures(string data, string url)
 {
 MatchCollection ps = Regex.Matches(data, @"<img\b[^<>]*?\bsrc[\s\t\r\n]*=[\s\t\r\n]*[""']?[\s\t\r\n]*(?<imgUrl>[^\s\t\r\n""'<>]*)[^<>]*?/?[\s\t\r\n]*>");
 string s = string.Empty;
 for (int i = 0; i < ps.Count; i++)
 {
 pictures p = new pictures(ps[i].Value, url);
 s += p.GetHtml + "<br />" + Environment.NewLine;
 }
 return s;
 }

 /// <summary>
 /// 圖片實體
 /// 圖片文件屬性處理類
 /// </summary>
 public class pictures
 {
 public pictures(string strHtml, string baseUrl)
 {
 _html = strHtml;
 Uri u1 = new Uri(baseUrl);
 _doman = u1.Host;
 _baseUrl = u1.Scheme + "://" + _doman;
 setSrc();
 }

 private string _html = string.Empty;
 private string _baseUrl = string.Empty;
 private string _doman = string.Empty;

 public string GetHtml
 {
 get { return _html; }
 }

 public string Alt
 {
 get
 {
 return GetAttribute("alt")[0];
 }
 }

 public string Src
 {
 get
 {
 string s = GetAttribute("src")[0];
 return s;
 }
 }

 /// <summary>
 /// 根據基路徑把相對路徑轉換成絕對徑
 /// </summary>
 /// <param name="baseUrl">基礎路徑</param>
 /// <param name="u">待轉換的相對路徑</param>
 /// <returns>絕對路徑</returns>
 public string absUrl(string baseUrl, string u)
 {
 Uri ub = new Uri(baseUrl);
 Uri ua = new Uri(ub, u);
 return ua.AbsoluteUri;
 }

 private void setSrc()
 {
 string strPattern = @"src[\s\t\r\n]*=[\s\t\r\n]*[""']?\S+[""']?";
 string src = GetAttribute("src")[0].ToLower();
 if (!(src.IndexOf("http://") == 0 || src.IndexOf("https://") == 0) && _baseUrl.Length > 10)
 {
 src = absUrl(_baseUrl, src);
 string s = "src=\"" + src + "\"";
 _html = Regex.Replace(_html, strPattern, s);
 }
 }

 /// <summary>
 /// 獲取HTML代碼中標簽屬性
 /// </summary>
 /// <param name="strHtml">HTML代碼</param>
 /// <param name="strAttributeName">屬性名稱</param>
 /// <returns>屬性值集合</returns>
 private string[] GetAttribute(string strAttributeName)
 {
 List<string> lstAttribute = new List<string>();
 string strPattern = string.Format(
 @"{0}[\s\t\r\n]*=[\s\t\r\n]*[""']?\S+[""']?",
 strAttributeName
 );
 MatchCollection matchs = Regex.Matches(_html, strPattern, RegexOptions.IgnoreCase);
 foreach (Match m in matchs)
 {
 lstAttribute.Add(m.Value.Split('=')[1].Replace("\"", "").Replace("'", ""));
 }
 if (lstAttribute.Count == 0) lstAttribute.Add("");
 return lstAttribute.ToArray();
 }
 }
 }

new WebPageImage().getImages(http://www.sina.com)