using System;
using System.IO;
using System.Net;
using System.Text.RegularExpressions;

/// <summary>
/// 图片下载
/// </summary>
public class ImageDown
{
    public ImageDown()
    { }

    #region 私有方法
    /// <summary>
    /// 获取图片标志
    /// </summary>
    private string[] GetImgTag(string htmlStr)
    {
        Regex regObj = new Regex("<img.+?>", RegexOptions.Compiled | RegexOptions.IgnoreCase);
        string[] strAry = new string[regObj.Matches(htmlStr).Count];
        int i = 0;
        foreach (Match matchItem in regObj.Matches(htmlStr))
        {
            strAry[i] = GetImgUrl(matchItem.Value);
            i++;
        }
        return strAry;
    }

    /// <summary>
    /// 获取图片URL地址
    /// </summary>
    private string GetImgUrl(string imgTagStr)
    {
        string str = "";
        Regex regObj = new Regex("http://.+.(?:jpg|gif|bmp|png)", RegexOptions.Compiled | RegexOptions.IgnoreCase);
        foreach (Match matchItem in regObj.Matches(imgTagStr))
        {
            str = matchItem.Value;
        }
        return str;
    }
    #endregion

    /// <summary>
    /// 下载图片到本地
    /// </summary>
    /// <param name="strHTML">HTML</param>
    /// <param name="path">路径</param>
    /// <param name="nowyymm">年月</param>
    /// <param name="nowdd">日</param>
    public string SaveUrlPics(string strHTML, string path)
    {
        string nowym = DateTime.Now.ToString("yyyy-MM");  //当前年月
        string nowdd = DateTime.Now.ToString("dd");       //当天号数
        path = path + nowym + "/" + nowdd;
        if (!Directory.Exists(path)) Directory.CreateDirectory(path);

        string[] imgurlAry = GetImgTag(strHTML);
        try
        {
            for (int i = 0; i < imgurlAry.Length; i++)
            {
                string preStr = System.DateTime.Now.ToString() + "_";
                preStr = preStr.Replace("-", "");
                preStr = preStr.Replace(":", "");
                preStr = preStr.Replace(" ", "");
                WebClient wc = new WebClient();
                wc.DownloadFile(imgurlAry[i], path + "/" + preStr + imgurlAry[i].Substring(imgurlAry[i].LastIndexOf("/") + 1));
            }
        }
        catch (Exception ex)
        {
            return ex.Message;
        }
        return strHTML;
    }
}

ImageDown