ASP.NET验证码C#

1、编写类CreateImage.cs
2、在页面Image.aspx中输出验证图片，即是调用函数：CreateImage.DrawImage();
3、在图片中使用：src=Image.aspx
4、检验Session：Session["CheckCode"]
以下是生成验证码的类：CreateImage.cs
using System;
using System.IO;
using System.Web;
using System.Drawing;
namespace ZCJ168.App_Code
{
    /// <summary>
    /// 验证码模块
    /// </summary>
    public class CreateImage
    {
        public static void DrawImage()
        {
            CreateImage img=new CreateImage();
            HttpContext.Current.Session["CheckCode"]=img.RndNum(5);
            img.CreateImages(HttpContext.Current.Session["CheckCode"].ToString());
        }

        /// <summary>
        /// 生成验证图片
        /// </summary>
        /// <param name="checkCode">验证字符</param>
        private void CreateImages(string checkCode)
        {
            int iwidth = (int)(checkCode.Length * 14);
            System.Drawing.Bitmap image = new System.Drawing.Bitmap(iwidth, 23);
            Graphics g = Graphics.FromImage(image);
            g.Clear(Color.White);
            //定义颜色
            Color[] c = {Color.Black,Color.Red,Color.DarkBlue,Color.Green,Color.Orange,Color.Brown,Color.DarkCyan,Color.Purple};
            //定义字体
            string[] font = {"Verdana","Microsoft Sans Serif","Comic Sans MS","Arial","宋体"};
            Random rand = new Random();
            //随机输出噪点
            for(int i=0;i<50;i++)
            {
                int x = rand.Next(image.Width);
                int y = rand.Next(image.Height);
                g.DrawRectangle(new Pen(Color.GreenYellow, 0),x,y,1,1);
            }

            //输出不同字体和颜色的验证码字符
            for(int i=0;i<checkCode.Length;i++)
            {
                int cindex = rand.Next(7);
                int findex = rand.Next(5);

                Font f = new System.Drawing.Font(font[findex], 10, System.Drawing.FontStyle.Bold);
                Brush b = new System.Drawing.SolidBrush(c[cindex]);
                int ii=4;
                if((i+1)%2==0)
                {
                    ii=2;
                }
                g.DrawString(checkCode.Substring(i,1), f, b, 3+(i*12), ii);
            }
            //画一个边框
            g.DrawRectangle(new Pen(Color.Black,0),0,0,image.Width-1,image.Height-1);

            //输出到浏览器
            System.IO.MemoryStream ms = new System.IO.MemoryStream();
            image.Save(ms,System.Drawing.Imaging.ImageFormat.Jpeg);
            HttpContext.Current.Response.ClearContent();
            //Response.ClearContent();
            HttpContext.Current.Response.ContentType = "image/Jpeg";
            HttpContext.Current.Response.BinaryWrite(ms.ToArray());
            g.Dispose();
            image.Dispose();
        }

        /// <summary>
        /// 生成随机的字符串
        /// </summary>
        /// <param name="VcodeNum">生成字母的个数</param>
        /// <returns>string</returns>
        private string RndNum(int VcodeNum)
        {
            string Vchar = "a,b,c,d,e,f,g,h,i,j,k,l,m,n,o,p,q,r,s,t,y,v,x,y,z,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,0,1,2,3,4,5,6,7,8,9" ;
            string[] VcArray = Vchar.Split(',') ;
            string VNum = "" ; //由于字符串很短，就不用StringBuilder了
            int temp = -1 ; //记录上次随机数值，尽量避免生产几个一样的随机数

            //采用一个简单的算法以保证生成随机数的不同
            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(VcArray.Length ) ;
                if (temp != -1 && temp == t)
                {
                    return RndNum( VcodeNum );
                }
                temp = t ;
                VNum += VcArray[t];
            }
            return VNum ;
        }
    }

}