程序代码：

  protected void btnUpload_Click(object sender, EventArgs e)
    {
        if (this.fileUploadImg.HasFile)
        {
            //图片大小
            int fileSize = this.fileUploadImg.PostedFile.ContentLength / (1024 * 1024);
            //全名 11aa.jpg
            string fullFileName = this.fileUploadImg.PostedFile.FileName;
            //后缀 .jpg
            string exName = Path.GetExtension(fullFileName);
            if (exName.Trim().ToLower().ToString() == ".jpg" || exName.Trim().ToLower().ToString() == ".png" || exName.Trim().ToLower().ToString() == ".gif")
            {
                if (fileSize <= 10)// 10M
                {
                    string savePath = Server.MapPath("UploadImgs/") + fullFileName;
                    this.fileUploadImg.PostedFile.SaveAs(savePath);
                    string showpath = "UploadImgs/" + fullFileName;
                    this.ImgShow.ImageUrl = showpath;
                    // 保存图片的名称
                    ViewState["ImgName"] = fullFileName;
                }
                else
                {
                    Page.RegisterStartupScript("", "<script>f_alert2('warn','图片大小不能超过" + fileSize + "！');</script>");
                    return;
                }
            }
            else
            {
                Page.RegisterStartupScript("", "<script>f_alert2('warn','请只上传jpg、.gif、.png格式的图片!');</script>");
                return;
            }
        }
        else
        {
            Page.RegisterStartupScript("", "<script>f_alert2('warn','请选择要上传的图片！'); </script>");
            return;
        }
    }
页面旁边有一个图片框用来显示图片，这段代码就是让图片显示到图片框中