<asp:Button 
	ID="DeleteButton" 
	runat="server" 
	CommandName="Delete" 
	Text="删除" 
	OnClientClick="return confirm('您确认要删除吗？')"
/>

<asp:TextBox ID="txtpwd" TextMode="Password" runat="server" ></asp:TextBox>

using System;
using System.Collections.Generic;
using System.Linq;
using System.Web;
using System.Web.UI;
using System.Web.UI.WebControls;
using System.IO;

namespace ex
{
    public partial class WebForm1 : System.Web.UI.Page
    {
       
        string fileName;  //图片名  
        string fileExt;   //图片扩展名
        string filePath;  //图片绝对路径
        string fileType;  //图片MIME类型
        double fileSize;  //图片大小（byte）
        string[] ext = new string[] { ".png", ".jpg", ".gif" };
        
        protected void Page_Load(object sender, EventArgs e)
        {
            Panel1.Visible = false;
        }
        
        //图片上传
        protected void Button1_Click(object sender, EventArgs e)
        {

            if (FileUpload1.HasFile)
            {
                fileName = FileUpload1.FileName;
                fileExt = Path.GetExtension(fileName);
                fileSize = FileUpload1.PostedFile.ContentLength;
                fileType = FileUpload1.PostedFile.ContentType;
                
                //此处根据自己的路径修改
                filePath = "C:\Users\AD\source\repos\WebApplication8\WebApplication8\image\" + fileName;
                if (fileExt == ext[0] || fileExt == ext[1] || fileExt == ext[2])
                {
                    try
                    {
                        FileUpload1.SaveAs(Server.MapPath("./image/") + fileName);
                        if (File.Exists(filePath))
                        {
                            Image1.ImageUrl = @"./image/" + fileName;
                            Response.Write("<script>alert('上传成功！');</script>");
                        }
                        else
                            Response.Write("<script>alert('图片上传成功，但图片不存在或已被删除！');</script>");
                    }
                    catch (Exception)
                    {
                        throw;
                    }
                    finally
                    {
                        Panel1.Visible = true;
                        Label1.Text = filePath;
                        Label2.Text = fileName;
                        Label3.Text = fileExt;
                        Label4.Text = Math.Round(fileSize / (1024 * 1024), 2).ToString() + "M";
                        Label5.Text = fileType;
                    }
                }
                else
                    Response.Write("<script>alert('请上传png、jpg、gif格式的图片！');</script>");
            }
            else
                Response.Write("<script>alert('请选择要上传图片！');</script>");
        }
    }
}