以下介绍两种方法：

1.利用WebRequest，WebResponse 类

WebRequest wreq=WebRequest.Create("http://files.jb51.net/file_images/article/201205/logo.gif");

HttpWebResponse wresp=(HttpWebResponse)wreq.GetResponse();

Stream s=wresp.GetResponseStream();

System.Drawing.Image img;

img = System.Drawing.Image.FromStream(s);

img.Save("D:aa.gif",ImageFormat.Gif); //保存

//下面直接输出

MemoryStream ms=new MemoryStream();

img.Save(ms,ImageFormat.Gif);

img.Dispose();

Response.ClearContent();

Response.ContentType="image/gif";

Response.BinaryWrite(ms.ToArray());

2.利用 WebClient 类

WebClient my=new WebClient();

byte[] mybyte;

mybyte=my.DownloadData("http://files.jb51.net/file_images/article/201205/logo.gif"); MemoryStream ms=new MemoryStream(mybyte);

System.Drawing.Image img;

img = System.Drawing.Image.FromStream(ms);

img.Save("D:a.gif",ImageFormat.Gif); //保存

//下面直接输出

Response.ClearContent();

Response.ContentType="image/gif";

Response.BinaryWrite(mybyte);

如果是真实的图片地址直接用

my.DownloadFile("http://files.jb51.net/file_images/article/201205/logo.gif","D:a.gif"); //保存

直接可以保存