c#中怎么用代码替换窗体的背景图片

this.BackgroundImage = Image.FromFile(@"http://himg.bdimg.com/sys/portrait/item/3cfde98499e8a786e78886e5a4b44923.jpg?cdnversion=3221");

this.Size = this.BackgroundImage.Size;

可以用代码实现网上的任意一个图片的替换窗体背景
------解决方案--------------------
WebClient.DownloadFile("http://himg.bdimg.com/sys/portrait/item/3cfde98499e8a786e78886e5a4b44923.jpg?cdnversion=3221", "1.jpg");
this.BackgroundImage?=?Image.FromFile("1.jpg");
this.Size?=?this.BackgroundImage.Size;