验证码的制作与校验（使用 cookie 传值）
（1）验证码应该是图片格式，不能是文字格式，即无法用鼠标选中。（2）验证码上应该有噪点和干扰线条。（3）验证码应该回避相似字符，如“0”和“o”“I”和“1”等。（4）验证码至少是数字和字母（含大小写）的组合，不应该是单纯的数字或字母，可以出现汉字。应该实现输入验证码字母字母“不区分大小写”。验证码中的内容，应该是随机生成。（5）验证码，可以通过点击图片或旁边文字实现“看不清，换一张”的功能。（6）应当有个用于核对验证码输入是否正确的tbx和btn，当点击btn时，弹窗提示验证码输入的是正确或错误。
一、效果
制作验证码主要是利用了C#的GDI绘制，效果如下图所示：
二、代码实现
项目资源分布
主页 WebForm1.aspx
<%@ Page Language="C#" AutoEventWireup="true" CodeBehind="WebForm1.aspx.cs" Inherits="ImageCode.WebForm1" %><!DOCTYPE html><html xmlns="/1999/xhtml"><head runat="server"><meta http-equiv="Content-Type" content="text/html; charset=utf-8" /><title></title></head><body><form id="form1" runat="server"><div><asp:Label ID="Label1" runat="server" Text="验证码:" Font-Size="25px"></asp:Label><asp:TextBox ID="tbx_imgcheckingcode" runat="server" Width="82px" Height="25px"></asp:TextBox><%-- ondblclick 事件在用户双击元素时发生。--%><asp:ImageButton ID="ibtn_imgcheckingcode" src="WebForm2.aspx" runat="server" Height="40px" Width="70px" οnclick="this.src=this.src+'?'" ToolTip="看不清我，就点一下我吧！" /><a href="javascript:changeCode()" style="text-decoration: underline; font-size: 10px;">换一张</a><br /><%-- 刷新验证码--%><script type="text/javascript">function changeCode() {document.getElementById('ibtn_imgcheckingcode').src = document.getElementById('ibtn_imgcheckingcode').src + '?';}</script><asp:Button ID="Button1" runat="server" Text="验证" OnClick="Button1_Click" /></div></form></body></html>
WebForm1.aspx.cs（注意 namespace 的引用，改成自己的项目名）
using System;using System.Collections.Generic;using System.Linq;using System.Web;using System.Web.UI;using System.Web.UI.WebControls;namespace ImageCode{public partial class WebForm1 : System.Web.UI.Page{protected void Page_Load(object sender, EventArgs e){//引入验证码 urlibtn_imgcheckingcode.ImageUrl = "WebForm2.aspx";}//使用cookie传值验证protected void Button1_Click(object sender, EventArgs e){string checkingcode = tbx_imgcheckingcode.Text;//收到cookie请求的对象HttpCookie cookie_checkingcode = Request.Cookies["ImageV"];//将验证码中的字母转为大写，进行校验string scode = cookie_checkingcode.Value.ToUpper().ToString();if (checkingcode.ToUpper()!= scode){Response.Write("<script>alert('验证码输入不正确！')</script>");}else{this.tbx_imgcheckingcode.Text = "";Response.Write("<script>alert('验证码输入正确')</script>");}}}}
验证码页面 WebForm2.aspx (什么都不用写)
<%@ Page Language="C#" AutoEventWireup="true" CodeBehind="WebForm2.aspx.cs" Inherits="ImageCode.WebForm2" %><!DOCTYPE html><html xmlns="/1999/xhtml"><head runat="server"><meta http-equiv="Content-Type" content="text/html; charset=utf-8"/><title></title></head><body><form id="form1" runat="server"><div></div></form></body></html>
WebForm2.aspx.cs
注意using引用
using System;using System.Collections.Generic;//引入画板using System.Drawing;using System.Drawing.Imaging;using System.IO;using System.Linq;using System.Web;using System.Web.UI;using System.Web.UI.WebControls;namespace ImageCode{public partial class WebForm2 : System.Web.UI.Page{protected void Page_Load(object sender, EventArgs e){string tmp = RndNum(4);//将验证码写入cookieHttpCookie a = new HttpCookie("ImageV", tmp);Response.Cookies.Add(a);this.ValidateCode(tmp);}private void ValidateCode(string VNum){//创建位图对象Bitmap Img = null;Graphics g = null//分配内存空间MemoryStream ms = null;int gheight = VNum.Length * 12;Img = new Bitmap(gheight, 25);g = Graphics.FromImage(Img);//生成随机生成器Random random = new Random();//背景颜色g.Clear(Color.White);//生成噪点随机颜色for (int i = 0; i < 100; i++){int x = random.Next(Img.Width);int y = random.Next(Img.Height);Img.SetPixel(x, y, Color.FromArgb(random.Next()));}//添加干扰线条int z =6;//干扰线条数for (int i = 0; i < z; i++){int x1 = random.Next(Img.Width);int x2 = random.Next(Img.Width);int y1 = random.Next(Img.Height);int y2 = random.Next(Img.Height);//随机干扰线条颜色int r = random.Next(255);int green = random.Next(255);int b = random.Next(255);g.DrawLine(new Pen(Color.FromArgb(r,green,b), 1), x1, y1, x2, y2);//根据坐标画线}//文字字体Font f = new Font("Arial Black ", 12);//文字颜色SolidBrush s = new SolidBrush(Color.Blue);//画验证码g.DrawString(VNum, f, s, 3, 3);ms = new MemoryStream();//将验证码图片存入内存流,并将其以 "image/Jpeg" 格式输出 Img.Save(ms, ImageFormat.Jpeg);Response.ClearContent();Response.ContentType = "image/Jpeg ";Response.BinaryWrite(ms.ToArray());//显式释放资源 g.Dispose();Img.Dispose();Response.End();}private string RndNum(int VcodeNum){// //定义存放的字符串回避相似字符string Vchar = "2,3,4,5,6,7,8,9,A,B,C,D,E,F,G,H,J,K,M,N,P" +",Q,R,S,T,U,V,W,X,Y,Z,a,b,c,d,e,f,g,h,g,k,m,n,p,q,r,s,t,u,v,w,x,y,z";string[] VcArray = Vchar.Split(new Char[] {',' });string VNum = " ";int temp = -1;Random rand = new Random();for (int i = 1; i < VcodeNum + 1; i++){if (temp != -1){rand = new Random(i * temp * unchecked((int)DateTime.Now.Ticks));}int t = rand.Next(54);if (temp != -1 && temp == t){return RndNum(VcodeNum);}temp = t;VNum += VcArray[t];}return VNum;}}}
