假如使用流输出一个图片，在下面代码加上输出时候的宽和高
FileStream FsImg = new FileStream(Server.MapPath("xx.gif" ), FileMode.Open);
  byte[] imgByte = new byte[FsImg.Length];
  FsImg.Read(imgByte, 0, imgByte.Length);
  FsImg.Close();
  Response.Clear();
  Response.OutputStream.Write(imgByte, 0, imgByte.Length);
  Response.End();

------解决方案--------------------
//将byte[]转换为Image
public Image ReadImage(byte[] bytes)
{
　　FileStream fs=new FileStream("imagetemp1",FileMode.Create,FileAccess.Write,FileShare.None);
　　foreach(byte a in bytes) 
　　{ 
　　　　fs.WriteByte(a); 
　　}
fs.Close();
fs=new FileStream("imagetemp1",FileMode.Open,FileAccess.Read,FileShare.None);
BinaryFormatter bf = new BinaryFormatter();
object obj=bf.Deserialize(fs);
　　fs.Close(); 
　　return (Image)obj;
}
 private byte[] GetThumbnailImage(System.Drawing.Image img)
{
byte[] imgByte;
float iScale = img.Height > img.Width ? (float)img.Height / 100 :(float)img.Width / 100;
img = img.GetThumbnailImage((int)(img.Width/iScale),(int)(img.Height/iScale), null, IntPtr.Zero);
MemoryStream memStream = new MemoryStream();
img.Save(memStream, System.Drawing.Imaging.ImageFormat.Jpeg);
memStream.Flush();
imgByte = memStream.ToArray();
return imgByte;
}