c#生成图片验证码，避免被软件识别的完美方案

  1 /// <summary>
  2     /// 生成随机码
  3     /// </summary>
  4     /// <param name="length">随机码个数</param>
  5     /// <returns></returns>
  6     private string CreateRandomCode(int length)
  7     {
  8         int rand;
  9         char code;
 10         string randomcode = String.Empty;
 11 
 12         //生成一定长度的验证码
 13         System.Random random = new Random();
 14         for (int i = 0; i < length; i++)
 15         {
 16             rand = random.Next();
 17 
 18             if (rand % 3 == 0)
 19             {
 20                 code = (char)('A' + (char)(rand % 26));
 21             }
 22             else
 23             {
 24                 code = (char)('0' + (char)(rand % 10));
 25             }
 26 
 27             randomcode += code.ToString();
 28         }
 29         return randomcode;
 30     }
 31 
 32     /// <summary>
 33     /// 创建随机码图片
 34     /// </summary>
 35     /// <param name="randomcode">随机码</param>
 36     private void CreateImage(string randomcode)
 37     {
 38         int randAngle = 45; //随机转动角度
 39         int mapwidth = (int)(randomcode.Length * 16);
 40         Bitmap map = new Bitmap(mapwidth, 22);//创建图片背景
 41         Graphics graph = Graphics.FromImage(map);
 42         graph.Clear(Color.AliceBlue);//清除画面，填充背景
 43         graph.DrawRectangle(new Pen(Color.Black, 0), 0, 0, map.Width - 1, map.Height - 1);//画一个边框
 44         //graph.SmoothingMode = System.Drawing.Drawing2D.SmoothingMode.AntiAlias;//模式
 45 
 46         Random rand = new Random();
 47 
 48         //背景噪点生成
 49         Pen blackPen = new Pen(Color.LightGray, 0);
 50         for (int i = 0; i < 50; i++)
 51         {
 52             int x = rand.Next(0, map.Width);
 53             int y = rand.Next(0, map.Height);
 54             graph.DrawRectangle(blackPen, x, y, 1, 1);
 55         }
 56 
 57 
 58         //验证码旋转，防止机器识别
 59         char[] chars = randomcode.ToCharArray();//拆散字符串成单字符数组
 60 
 61         //文字距中
 62         StringFormat format = new StringFormat(StringFormatFlags.NoClip);
 63         format.Alignment = StringAlignment.Center;
 64         format.LineAlignment = StringAlignment.Center;
 65 
 66         //定义颜色
 67         Color[] c = { Color.Black, Color.Red, Color.DarkBlue, Color.Green, Color.Orange, Color.Brown, Color.DarkCyan, Color.Purple };
 68         //定义字体
 69         string[] font = { "Verdana", "Microsoft Sans Serif", "Comic Sans MS", "Arial", "宋体" };
 70         int cindex = rand.Next(7);
 71 
 72         for (int i = 0; i < chars.Length; i++)
 73         {
 74             int findex = rand.Next(5);
 75 
 76             Font f = new System.Drawing.Font(font[findex], 14, System.Drawing.FontStyle.Bold);//字体样式(参数2为字体大小)
 77             Brush b = new System.Drawing.SolidBrush(c[cindex]);
 78 
 79             Point dot = new Point(14, 14);
 80             //graph.DrawString(dot.X.ToString(),fontstyle,new SolidBrush(Color.Black),10,150);//测试X坐标显示间距的
 81             float angle = rand.Next(-randAngle, randAngle);//转动的度数
 82 
 83             graph.TranslateTransform(dot.X, dot.Y);//移动光标到指定位置
 84             graph.RotateTransform(angle);
 85             graph.DrawString(chars[i].ToString(), f, b, 1, 1, format);
 86             //graph.DrawString(chars[i].ToString(),fontstyle,new SolidBrush(Color.Blue),1,1,format);
 87             graph.RotateTransform(-angle);//转回去
 88             graph.TranslateTransform(-2, -dot.Y);//移动光标到指定位置，每个字符紧凑显示，避免被软件识别
 89         }
 92         //生成图片
 93         System.IO.MemoryStream ms = new System.IO.MemoryStream();
 94         map.Save(ms, System.Drawing.Imaging.ImageFormat.Gif);
 95         Response.ClearContent();
 96         Response.ContentType = "image/gif";
 97         Response.BinaryWrite(ms.ToArray());
 98         graph.Dispose();
 99         map.Dispose();
100     }

最近公司做一个投票系统，为了避免刷票机自动刷票；在投票按钮上要求输入验证码；

受到QQ网站验证码的启发；经过多次试验，本方案能避免被软件识别；

现在发出来分享。