[转]c#登陆实现验证码-图形编程

protected void Page_Load(object sender, EventArgs e)
        {
            // 创建一个包含随机内容的验证码文本
            System.Random rand = new Random();
            int len = rand.Next(4, 6);
            char[] chars = "0123456789ABCDEFGHIJKLMNOPQRSTUVWXYZ".ToCharArray();
            System.Text.StringBuilder myStr = new System.Text.StringBuilder();
            for (int iCount = 0; iCount < len; iCount++)
            {
                myStr.Append(chars[rand.Next(chars.Length)]);
            }

            string text = myStr.ToString();
            // 保存验证码到 session 中以便其他模块使用
            this.Session["checkcode"] = text;

            Size ImageSize = Size.Empty;
            Font myFont = new Font("MS Sans Serif", 20);

            // 计算验证码图片大小
            using (Bitmap bmp = new Bitmap(10, 10))
            {
                using (Graphics g = Graphics.FromImage(bmp))
                {
                    SizeF size = g.MeasureString(text, myFont, 10000);
                    ImageSize.Width = (int)size.Width + 8;
                    ImageSize.Height = (int)size.Height + 8;
                }
            }

            // 创建验证码图片
            using (Bitmap bmp = new Bitmap(ImageSize.Width, ImageSize.Height))
            {
                // 绘制验证码文本
                using (Graphics g = Graphics.FromImage(bmp))
                {
                    g.Clear(Color.White);
                    using (StringFormat f = new StringFormat())
                    {
                        f.Alignment = StringAlignment.Near;
                        f.LineAlignment = StringAlignment.Center;
                        f.FormatFlags = StringFormatFlags.NoWrap;
                        g.DrawString(
                            text,
                            myFont,
                            Brushes.Black,
                            new RectangleF(
                            0,
                            0,
                            ImageSize.Width,
                            ImageSize.Height),
                            f);
                    }//using
                }//using

                // 制造噪声 杂点面积占图片面积的 30%
                int num = ImageSize.Width * ImageSize.Height * 30 / 100;

                for (int iCount = 0; iCount < num; iCount++)
                {
                    // 在随机的位置使用随机的颜色设置图片的像素
                    int x = rand.Next(ImageSize.Width);
                    int y = rand.Next(ImageSize.Height);
                    int r = rand.Next(255);
                    int g = rand.Next(255);
                    int b = rand.Next(255);
                    Color c = Color.FromArgb(r, g, b);
                    bmp.SetPixel(x, y, c);
                }//for                // 输出图片
                System.IO.MemoryStream ms = new System.IO.MemoryStream();
                bmp.Save(ms, System.Drawing.Imaging.ImageFormat.Png);
                this.Response.ContentType = "image/png";
                ms.WriteTo(this.Response.OutputStream);
                ms.Close();

            }//using            
              myFont.Dispose();

        }//private void Page_Load(object sender, System.EventArgs e)


    //别忘了 Systm.Drawing;

另,如果验证码是汉字的话,可以使用以下代码:

using System.Text; 

namespace ConsoleApplication 
{ 
    class ChineseCode 
　　{ 
        public static void Main() 
        { 
            //获取GB2312编码页（表） 
            Encoding gb=Encoding.GetEncoding("gb2312"); 

            //调用函数产生4个随机中文汉字编码 
            object[] bytes=CreateRegionCode(4); 

            //根据汉字编码的字节数组解码出中文汉字 
            string str1=gb.GetString((byte[])Convert.ChangeType(bytes[0], typeof(byte[]))); 
            string str2=gb.GetString((byte[])Convert.ChangeType(bytes[1], typeof(byte[]))); 
            string str3=gb.GetString((byte[])Convert.ChangeType(bytes[2], typeof(byte[]))); 
            string str4=gb.GetString((byte[])Convert.ChangeType(bytes[3], typeof(byte[]))); 

            //输出的控制台 
　　        Console.WriteLine(str1 + str2 +str3 +str4); 
　　    } 


        /**//* 
        此函数在汉字编码范围内随机创建含两个元素的十六进制字节数组，每个字节数组代表一个汉字，并将 
        四个字节数组存储在object数组中。 
        参数：strlength，代表需要产生的汉字个数 
        */ 
        public static object[] CreateRegionCode(int strlength) 
        { 
            //定义一个字符串数组储存汉字编码的组成元素 
            string[] rBase=new String [16]{"0","1","2","3","4","5","6","7","8","9","a","b","c","d","e","f"}; 
            
            Random rnd=new Random(); 
        
            //定义一个object数组用来 
            object[] bytes=new object[strlength]; 

            /**//*每循环一次产生一个含两个元素的十六进制字节数组，并将其放入bject数组中 
            每个汉字有四个区位码组成 
            区位码第1位和区位码第2位作为字节数组第一个元素 
            区位码第3位和区位码第4位作为字节数组第二个元素 
            */ 
            for(int i=0;i <strlength;i++) 
            { 
                //区位码第1位 
                int r1=rnd.Next(11,14); 
                string str_r1=rBase[r1].Trim(); 

                //区位码第2位 
                rnd=new Random(r1*unchecked((int)DateTime.Now.Ticks)+i);//更换随机数发生器的 

种子避免产生重复值 
                int r2; 
                if (r1==13) 
                { 
                    r2=rnd.Next(0,7); 
                } 
                else 
                { 
                    r2=rnd.Next(0,16); 
                } 
                string str_r2=rBase[r2].Trim(); 

                //区位码第3位 
                rnd=new Random(r2*unchecked((int)DateTime.Now.Ticks)+i); 
                int r3=rnd.Next(10,16); 
                string str_r3=rBase[r3].Trim(); 

                //区位码第4位 
                rnd=new Random(r3*unchecked((int)DateTime.Now.Ticks)+i); 
                int r4; 
                if (r3==10) 
                { 
                    r4=rnd.Next(1,16); 
                } 
                else if (r3==15) 
                { 
                    r4=rnd.Next(0,15); 
                } 
                else 
                { 
                    r4=rnd.Next(0,16); 
                } 
                string str_r4=rBase[r4].Trim(); 

                //定义两个字节变量存储产生的随机汉字区位码 
                byte byte1=Convert.ToByte(str_r1 + str_r2,16); 
                byte byte2=Convert.ToByte(str_r3 + str_r4,16); 
                //将两个字节变量存储在字节数组中 
                byte[] str_r=new byte[]{byte1,byte2}; 

                //将产生的一个汉字的字节数组放入object数组中 
                bytes.SetValue(str_r,i); 
                
            } 

            return bytes; 

            } 
　　} 

}