页面

using System;using System.Configuration;using System.Data;using System.Linq;using System.Web;using System.Web.Security;using System.Web.UI;using System.Web.UI.HtmlControls;using System.Web.UI.WebControls;using System.Web.UI.WebControls.WebParts;using System.Xml.Linq;using System.Drawing;  namespace AMPlatForm.Union.Online{    public partial class ValiCode : System.Web.UI.Page    {        protected void Page_Load(object sender, EventArgs e)        {            DoImg(DoCode(5));        }        /// 
        /// 生成验证码表达式        /// 
        /// 验证码的长度        /// 
     
      验证码表达式
             private string DoCode(int num)        {            //要从这个数组中随机取字符来生成验证码            string[] Codesource ={
   "0","1","2","3","4","5","6","7","8","9",                             "a","b","c","d","e","f","g","h","i","j","k","l","m","n","o","p","q","r","s","t","u","v","w","x","y","z"};            string code = "";            Random rd = new Random();            for (int i = 0; i < num; i++)            {                code += Codesource[rd.Next(0, Codesource.Length)];            }            return code;        }        /// 
        /// 生成图片        /// 
        /// 验证码表达式        private void DoImg(string code)        {            Random random = new Random();            Bitmap mypalette = new Bitmap(100, 30);            Graphics gh = Graphics.FromImage(mypalette);            using (gh)            {                Rectangle rc = new Rectangle(0, 0, 100, 30);                //填充图片                gh.FillRectangle(new SolidBrush(Color.White), rc);                for (int i = 0; i < 1; i++)                {                    int x1 = random.Next(mypalette.Width);                    int x2 = random.Next(mypalette.Width);                    int y1 = random.Next(mypalette.Height);                    int y2 = random.Next(mypalette.Height);                    //在图片上随机画线条                    gh.DrawLine(new Pen(Color.Blue), x1, y1, x2, y2);                }                gh.DrawString(code, new Font("宋体", 20), new SolidBrush(Color.Black), rc);                for (int i = 1; i < 60; i++)                {                    int x = random.Next(mypalette.Width);                    int y = random.Next(mypalette.Height);                    //在图片中填充随机颜色                    mypalette.SetPixel(x, y, Color.FromArgb(random.Next()));                }                //将生成的图像保存到流中                mypalette.Save(Response.OutputStream, System.Drawing.Imaging.ImageFormat.Jpeg);                Session["ValiCode"] = code;         //主要用来验证            }            Response.Write(code);        }    }}

 前端局部刷新

<%@ Page Language="C#" AutoEventWireup="true" CodeBehind="WebForm3.aspx.cs" Inherits="Test.WebForm3" %>        
     
    
      
     
       
            
        
验证码测试
请输入验证码：
                    
          
        刷新验证码            
                
       
    
      
    
     
    

注意加参数

图片自己刷新

    
     
    
      
     
       
            
        
验证码测试
请输入验证码：