ms = new MemoryStream();解决方案

graphic.DrawImage(original_image, paste_x, paste_y, new_width, new_height);  //载入原始图，按指定大小重新绘制                        // Store the thumbnail in the session (Note: this is bad, it will take a lot of memory, but this is just a demo)            ms = new MemoryStream();            final_image.Save(ms, System.Drawing.Imaging.ImageFormat.Jpeg);//不明白，这里并没有建立什么联系？？？

using System;using System.Data;using System.Configuration;using System.Collections;using System.Web;using System.Web.Security;using System.Web.UI;using System.Web.UI.WebControls;using System.Web.UI.WebControls.WebParts;using System.Web.UI.HtmlControls;using System.IO;using System.Collections.Generic;public partial class upload : System.Web.UI.Page{    protected void Page_Load(object sender, EventArgs e)    {                System.Drawing.Image thumbnail_image = null;        System.Drawing.Image original_image = null;        System.Drawing.Bitmap final_image = null;        System.Drawing.Graphics graphic = null;        MemoryStream ms = null;        try        {            // Get the data  得到上传的文件            HttpPostedFile jpeg_image_upload = Request.Files["Filedata"];            // Retrieve the uploaded image  把上传文件转化为 Image            original_image = System.Drawing.Image.FromStream(jpeg_image_upload.InputStream);            // Calculate the new width and height 下边一整段，都是计算长宽的,具体算法没有深究            int width = original_image.Width;     //原始宽度            int height = original_image.Height;   //原始长度            int target_width = 200;            int target_height = 200;            int new_width, new_height;            float target_ratio = (float)target_width / (float)target_height;  //目标 宽长比            float image_ratio = (float)width / (float)height;   //原始  宽长比            if (target_ratio > image_ratio)   //计算出新的长宽。             {                new_height = target_height;                new_width = (int)Math.Floor(image_ratio * (float)target_height);            }            else            {                new_height = (int)Math.Floor((float)target_width / image_ratio);                new_width = target_width;            }            new_width = new_width > target_width ? target_width : new_width;            new_height = new_height > target_height ? target_height : new_height;                                    // Create the thumbnail  创建缩略图                        // Old way            //thumbnail_image = original_image.GetThumbnailImage(new_width, new_height, null, System.IntPtr.Zero);                // We don't have to create a Thumbnail since the DrawImage method will resize, but the GetThumbnailImage looks better                // I've read about a problem with GetThumbnailImage. If a jpeg has an embedded thumbnail it will use and resize it which                //  can result in a tiny 40x40 thumbnail being stretch up to our target size                        final_image = new System.Drawing.Bitmap(target_width, target_height);  //创建指定大小的位图            graphic = System.Drawing.Graphics.FromImage(final_image);              //为什么要通过Bitmap转一下?  应该是可以动态画画            //黑色的画笔,在graphic内画一个指定的矩形            graphic.FillRectangle(new System.Drawing.SolidBrush(System.Drawing.Color.Black), new System.Drawing.Rectangle(0, 0, target_width, target_height));            int paste_x = (target_width - new_width) / 2;            int paste_y = (target_height - new_height) / 2;            graphic.InterpolationMode = System.Drawing.Drawing2D.InterpolationMode.HighQualityBicubic; /* new way */ //一个图像插值算法            //graphic.DrawImage(thumbnail_image, paste_x, paste_y, new_width, new_height);            graphic.DrawImage(original_image, paste_x, paste_y, new_width, new_height);  //载入原始图，按指定大小重新绘制                        // Store the thumbnail in the session (Note: this is bad, it will take a lot of memory, but this is just a demo)            ms = new MemoryStream();            final_image.Save(ms, System.Drawing.Imaging.ImageFormat.Jpeg);//不明白，这里并没有建立什么联系？？？            // Store the data in my custom Thumbnail object            string thumbnail_id = DateTime.Now.ToString("yyyyMMddHHmmssfff");  //设置文件名            Thumbnail thumb = new Thumbnail(thumbnail_id, ms.GetBuffer());            // Put it all in the Session (initialize the session if necessary)                        List<Thumbnail> thumbnails = Session["file_info"] as List<Thumbnail>;            if (thumbnails == null)            {                thumbnails = new List<Thumbnail>();                Session["file_info"] = thumbnails;            }            thumbnails.Add(thumb);            Response.StatusCode = 200;            Response.Write(thumbnail_id);        }        catch        {            // If any kind of error occurs return a 500 Internal Server error            Response.StatusCode = 500;            Response.Write("An error occured");            Response.End();        }        finally        {            // Clean up            if (final_image != null) final_image.Dispose();            if (graphic != null) graphic.Dispose();            if (original_image != null) original_image.Dispose();            if (thumbnail_image!= null )thumbnail_image.Dispose();            if (ms != null) ms.Close();            Response.End();        }        }}