验证码

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本文介绍了一个使用 ASP.NET 实现的简单验证码生成模块。该模块通过随机生成字母数字组合并绘制为图像来创建验证码，同时利用 Session 存储验证码值以供后续验证。

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using System;
using System.Data;
using System.Configuration;
using System.Web;
using System.Web.Security;
using System.Web.UI;
using System.Web.UI.WebControls;
using System.Web.UI.WebControls.WebParts;
using System.Web.UI.HtmlControls;
using System.Drawing;

public partial class Default3 : System.Web.UI.Page
{
    protected void Page_Load(object sender, EventArgs e)
    {
        CreateImage cc = new CreateImage();
        cc.DrawImage();

    }

    /// <summary>
    /// 验证码模块
    /// </summary>
    public class CreateImage
    {
        public void DrawImage()
        {
            CreateImage img = new CreateImage();
            HttpContext.Current.Session["CheckCode"] = img.RndNum(4);
            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 * 13);
            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.LightGray, 1), 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 = 5;
                if ((i + 1) % 2 == 0)
                {
                    ii = 1;
                }
                g.DrawString(checkCode.Substring(i, 1), f, b, 3 + (i * 12), ii);//
            }
            //画一个边框
            g.DrawRectangle(new Pen(Color.Black, 1), 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>
        /// 生成随机的字母
        /// </summary>
        /// <param name="VcodeNum">生成字母的个数</param>
        /// <returns>string</returns>
        private string RndNum(int VcodeNum)
        {
            string Vchar = "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,a,b,c,d,e,f,g,h,i,j,k,m,n,o,p,q,r,s,t,u,v,w,x,y,z";
            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;
        }
    }
}
原文：http://www.blogcn.com/user61/slqwell/index.html?filelist=1#md