//新添加命名空间  
using System.Net;  
using System.IO;
using System.Text.RegularExpressions;  //正则表达式

private void button1_Click(object sender, EventArgs e)
{
    webBrowser1.Navigate(textBox1.Text.Trim());         //显示网页
}

<strong>//定义num记录listBox2中获取到的图片URL个数
public int num = 0;
//点击"获取"按钮
private void button2_Click(object sender, EventArgs e)
{
    HtmlElement html = webBrowser1.Document.Body;      //定义HTML元素
    string str = html.OuterHtml;                       //获取当前元素的HTML代码
    MatchCollection matches;                           //定义正则表达式匹配集合
    //清空
    listBox1.Items.Clear();
    listBox2.Items.Clear();
    //获取
    try
    {          
        //正则表达式获取<a href></a>内容url
        matches = Regex.Matches(str, "<a href=\"([^\"]*?)\".*?>(.*?)</a>", RegexOptions.IgnoreCase);
        foreach (Match match in matches)
        {
            listBox1.Items.Add(match.Value.ToString());     
        }
        //正则表达式获取<img src=>图片url
        matches = Regex.Matches(str, @"<img\b[^<>]*?\bsrc[\s\t\r\n]*=[\s\t\r\n]*[""']?[\s\t\r\n]*(?<imgUrl>[^\s\t\r\n""'<>]*)[^<>]*?/?[\s\t\r\n]*>", RegexOptions.IgnoreCase);
        foreach (Match match in matches)
        {
            listBox2.Items.Add(match.Value.ToString());
        }
        //记录图片总数
        num = listBox2.Items.Count;
    }
    catch (Exception msg)
    {
        MessageBox.Show(msg.Message);    //异常处理
    }
}</strong>

//点击"下载"实现下载图片
private void button3_Click(object sender, EventArgs e)
{
    string imgsrc = string.Empty;             //定义
    //循环下载
    for (int j = 0; j < num; j++)
    {
        string content = listBox2.Items[j].ToString();    //获取图片url
        Regex reg = new Regex(@"<img.*?src=""(?<src>[^""]*)""[^>]*>", RegexOptions.IgnoreCase);
        MatchCollection mc = reg.Matches(content);        //设定要查找的字符串
        foreach (Match m in mc)
        {                
            try
            {
                WebRequest request = WebRequest.Create(m.Groups["src"].Value);//图片src内容
                WebResponse response = request.GetResponse();
                //文件流获取图片操作
                Stream reader = response.GetResponseStream();
                string path = "E://" + j.ToString() + ".jpg";        //图片路径命名 
                FileStream writer = new FileStream(path, FileMode.OpenOrCreate, FileAccess.Write);
                byte[] buff = new byte[512];
                int c = 0;                                           //实际读取的字节数   
                while ((c = reader.Read(buff, 0, buff.Length)) > 0)
                {
                    writer.Write(buff, 0, c);
                }
                //释放资源
                writer.Close();
                writer.Dispose();
                reader.Close();
                reader.Dispose();
                response.Close();
                //下载成功
                listBox2.Items.Add(path + ":图片保存成功!"); 
            }
            catch (Exception msg)
            {
                MessageBox.Show(msg.Message);
            }
        }
    }
}

/// <summary> 
/// 取得HTML中所有图片的 URL
/// </summary> 
/// <param name="sHtmlText">HTML代码</param> 
/// <returns>图片的URL列表</returns> 
public static string[] GetHtmlImageUrlList(string sHtmlText)
{
    // 定义正则表达式用来匹配 img 标签 
    Regex regImg = new Regex(@"<img\b[^<>]*?\bsrc[\s\t\r\n]*=[\s\t\r\n]*[""']?[\s\t\r\n]*(?<imgUrl>[^\s\t\r\n""'<>]*)[^<>]*?/?[\s\t\r\n]*>", RegexOptions.IgnoreCase);
    // 搜索匹配的字符串 
    MatchCollection matches = regImg.Matches(sHtmlText);
    int i = 0;
    string[] sUrlList = new string[matches.Count];
    // 取得匹配项列表 
    foreach (Match match in matches)
    {
        sUrlList[i++] = match.Groups["imgUrl"].Value;
    }
    return sUrlList;
}

/// <summary>
/// 获得图片的路径并存放
/// </summary>
/// <param name="M_Content">要检索的内容</param>
/// <returns>IList</returns>
public static IList<string> GetPicPath(string M_Content)
{
    IList<string> im = new List<string>();//定义一个泛型字符类
    Regex reg = new Regex(@"<img.*?src=""(?<src>[^""]*)""[^>]*>", RegexOptions.IgnoreCase);
    MatchCollection mc = reg.Matches(M_Content); //设定要查找的字符串
    foreach (Match m in mc)
    {
        im.Add(m.Groups["src"].Value);
    }
    return im;
}