从网络获取图片本地保存

http://www.tc5u.com/csharp/2144235.htm

http://www.sharejs.com/codes/csharp/2122

http://blog.csdn.net/hcf_force/article/details/21173343

https://msdn.microsoft.com/en-us/library/system.drawing.bitmap.aspx

http://stackoverflow.com/questions/12960670/read-write-using-stream-readbyte-and-stream-writebyte-in-c-sharp

http://www.cnblogs.com/skyivben/archive/2009/05/26/1489244.html