//第一个例子
protected void Page_Load(object sender, EventArgs e)
{
    // 文件路径
    string path = "/images/head.png";
    // 文件名
    string filename = "head.png";
 
    // 输出的是图片
    Response.ContentType = "image/png";
    // 添加头信息,为"文件下载/另存为"对话框指定默认文件名 
    Response.AddHeader("Content-Disposition", "filename=" + HttpUtility.UrlEncode(System.Text.Encoding.UTF8.GetBytes(filename)));
    Response.WriteFile(path);
    Response.End();
}
 
//第二个例子
 protected void Page_Load(object sender, EventArgs e)
        {
            try
            {
                string fileName = Request["ReInspectDoc"];
                string strSql = "SELECT fpath FROM AOI_Feedstock_Add_Record WHERE InspectionOrderNumber =#[STRING] ";
                DataTable dt = DBCenter.GetDataTable(strSql, fileName);
                if (string.IsNullOrWhiteSpace(dt.Rows[0][0].ToString().Trim()))
                {
                    throw new Exception("该单号没有对应的图片");
                }
                string prctureName = dt.Rows[0][0].ToString().Replace("/", "\\");
                picturePath = Server.MapPath(".") + "\\" + prctureName;
                // 输出的是图片
                Response.ContentType = prctureName;
                // 添加头信息,为"文件下载/另存为"对话框指定默认文件名 
                Response.AddHeader("Content-Disposition", "filename=" + HttpUtility.UrlEncode(System.Text.Encoding.UTF8.GetBytes(prctureName)));
                Response.WriteFile(picturePath);
               // Response.End();
                HttpContext.Current.ApplicationInstance.CompleteRequest();
            }
            catch (Exception ex)
            {
                throw new Exception(ex.ToString()+"该单号没有对应的图片");
            }
        }