设置登录时的图形验证码

首先建一个一般处理程序，命名为RandomCode.ashx

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Collections;
using System.Configuration;
using System.Data;
using System.Web;
using System.Web.UI;
using System.Web.UI.WebControls;
using System.Web.UI.WebControls.WebParts;
using System.Web.UI.HtmlControls;
using System.Drawing;

namespace IntegritySystem.Web.Tools
{
    /// <summary>
    /// RandomCode 的摘要说明
    /// </summary>
    public class RandomCode : IHttpHandler, System.Web.SessionState.IRequiresSessionState
    {
        public void ProcessRequest(HttpContext context)
        {
            string checkCode = GetRandomCode(5);
            context.Session["CheckCode"] = checkCode;
            SetPageNoCache();
            CreateImage(checkCode);
        }
        //获取验证码各个字母
        private string GetRandomCode(int CodeCount)
        {
            string allChar = "0,1,2,3,4,5,6,7,8,9,A,B,C,D,E,F,G,H,i,J,K,M,N,P,Q,R,S,T,U,W,X,Y,Z";
            string[] allCharArray = allChar.Split(',');
            string RandomCode = "";
            int temp = -1;
            Random rand = new Random();
            for (int i = 0; i < CodeCount; i++)
            {
                if (temp != -1)
                {
                    rand = new Random(temp * i * ((int)DateTime.Now.Ticks));
                }
                int t = rand.Next(33);
                while (temp == t)
                {
                    t = rand.Next(33);
                }
                temp = t;
                RandomCode += allCharArray[t];
            }
            return RandomCode;
        }

        //页面设置没有缓存
        private void SetPageNoCache()
        {
           HttpContext.Current.Response.Buffer = true;
           HttpContext.Current.Response.ExpiresAbsolute = System.DateTime.Now.AddSeconds(-1);
           HttpContext.Current.Response.Expires = 0;
           HttpContext.Current.Response.CacheControl = "no-cache";
           HttpContext.Current.Response.AppendHeader("Pragma", "No-Cache");
        }

        //设置背景图片
        private void CreateImage(string checkCode)
        {
            int iwidth = (int)(checkCode.Length * 14);
            System.Drawing.Bitmap image = new System.Drawing.Bitmap(iwidth, 30);
            Graphics g = Graphics.FromImage(image);
            Font f = new System.Drawing.Font("Arial", 15);
            Brush b = new System.Drawing.SolidBrush(Color.Black);
            Brush r = new System.Drawing.SolidBrush(Color.FromArgb(166, 8, 8));
            g.Clear(System.Drawing.ColorTranslator.FromHtml("#fff"));//背景色
            char[] ch = checkCode.ToCharArray();
            for (int i = 0; i < ch.Length; i++)
            {
                if (ch[i] >= '0' && ch[i] <= '9')
                {
                    g.DrawString(ch[i].ToString(), f, r, 8 + (i * 12), 3);
                }
                else
                {
                    g.DrawString(ch[i].ToString(), f, b, 3 + (i * 12), 3);
                }
            }
            System.IO.MemoryStream ms = new System.IO.MemoryStream();
            image.Save(ms, System.Drawing.Imaging.ImageFormat.Jpeg);
            HttpContext.Current.Response.Cache.SetNoStore();
            HttpContext.Current.Response.ClearContent();
            HttpContext.Current.Response.ContentType = "image/Jpeg";
            HttpContext.Current.Response.BinaryWrite(ms.ToArray());
            g.Dispose();
            image.Dispose();
        }
        public bool IsReusable
        {
            get
            {
                return false;
            }
        }
    }
}

然后前台调用：

 　　　　　　　　　　<input type="text" class="yzm" id="Codes" name="Codes" maxlength="6" style=" 80px;
                        float: left;" />
                    <img id="codeimg" alt="验证码" src="/Tools/RandomCode.ashx" title="点击" style=" margin-bottom:-5px; cursor:pointer;"
                         onclick="EditCode(this)"/>

脚本点击事件：

 function EditCode() {
        document.getElementById("codeimg").src="/Tools/RandomCode.ashx?id="+Math.random();
    }

在就是后台验证就可以了：

　　　　　　　　　　if (Session["CheckCode"] != null)
                {
                    if (Codes.ToLower() != Session["CheckCode"].ToString().ToLower())
                    {
                        Message = "验证码输入错误，请输入正确的验证码!";
                        return Json(new { Success = b, ErrorMessage = Message }, JsonRequestBehavior.AllowGet);
                    }
                }
                else
                {
                    Message = "验证码输入错误，请输入正确的验证码!";
                    return Json(new { Success = b, ErrorMessage = Message }, JsonRequestBehavior.AllowGet);
                }

效果就是这样了，验证码个数可以调整：