在幾年前，很多的網站是沒有驗證碼的，沒有驗證碼是件很痛苦的事，因爲對於一般用戶來說驗證碼只是增加了用戶的操作，降低了用戶的體驗。但是後來各種灌水機器人、投票機器人、惡意註冊機器人層出不窮，大大增加了網站的負擔同時也給網站數據庫帶來了大量的垃圾數據。爲了防止各種機器人程序的破壞，於是程序員想出了只有人眼能夠識別的，程序不容易識別的驗證碼！
所謂的驗證碼是一個圖片，將字母、數字甚至漢字作爲圖片的內容，這樣一張圖片中的內容用人眼很容易識別，而程序將無法識別。在進行數據庫操作之前（比如登錄驗證、投票、發帖、回覆、註冊等等）程序首先驗證客戶端提交的驗證碼是否與圖片中的內容相同，如果相同則進行數據庫操作，不同則提示驗證碼錯誤，不進行數據庫操作。這樣各種機器人程序就被拒之門外了！
但是隨着計算機科學的發展，模式識別等技術越來越成熟，於是編寫機器人程序的傢伙可以通過程序將直接寫在圖片中的內容識別出來，然後提交到服務器，這樣驗證碼將形同虛設。爲了防止機器人程序的識別，驗證碼的圖片生成也不斷在發展，加入干擾點、干擾線，文字變形、變換角度位置，顏色不同……各種防止計算機識別的技術也應用到驗證碼中。就在這兩種技術的競爭中，於是便形成了我們現在看到的驗證碼，已經有很多人在抱怨“這是什麼驗證碼哦，人眼都分辨不清楚是什麼”，一切也是無奈。
using System;
using System.Web;using System.Drawing;
using System.Security.Cryptography;
namespace DotNet.Utilities
{
/// <summary>
/// 驗證碼類
/// </summary>
public class Rand
{
#region 生成隨機數字
/// <summary>
/// 生成隨機數字
/// </summary>
/// <param name="length">生成長度</param>
public static string Number(int Length)
{
return Number(Length, false);
}
/// <summary>
/// 生成隨機數字
/// </summary>
/// <param name="Length">生成長度</param>
/// <param name="Sleep">是否要在生成前將當前線程阻止以避免重複</param>
public static string Number(int Length, bool Sleep)
{
if (Sleep) System.Threading.Thread.Sleep(3);
string result = "";
System.Random random = new Random();
for (int i = 0; i < Length; i++)
{
result += random.Next(10).ToString();
}
return result;
}
#endregion
#region 生成隨機字母與數字
/// <summary>
/// 生成隨機字母與數字
/// </summary>
/// <param name="IntStr">生成長度</param>
public static string Str(int Length)
{
return Str(Length, false);
}
/// <summary>
/// 生成隨機字母與數字
/// </summary>
/// <param name="Length">生成長度</param>
/// <param name="Sleep">是否要在生成前將當前線程阻止以避免重複</param>
public static string Str(int Length, bool Sleep)
{
if (Sleep) System.Threading.Thread.Sleep(3);
char[] Pattern = new char[] { '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' };
string result = "";
int n = Pattern.Length;
System.Random random = new Random(~unchecked((int)DateTime.Now.Ticks));
for (int i = 0; i < Length; i++)
{
int rnd = random.Next(0, n);
result += Pattern[rnd];
}
return result;
}
#endregion
#region 生成隨機純字母隨機數
/// <summary>
/// 生成隨機純字母隨機數
/// </summary>
/// <param name="IntStr">生成長度</param>
public static string Str_char(int Length)
{
return Str_char(Length, false);
}
/// <summary>
/// 生成隨機純字母隨機數
/// </summary>
/// <param name="Length">生成長度</param>
/// <param name="Sleep">是否要在生成前將當前線程阻止以避免重複</param>
public static string Str_char(int Length, bool Sleep)
{
if (Sleep) System.Threading.Thread.Sleep(3);
char[] Pattern = new char[] { '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' };
string result = "";
int n = Pattern.Length;
System.Random random = new Random(~unchecked((int)DateTime.Now.Ticks));
for (int i = 0; i < Length; i++)
{
int rnd = random.Next(0, n);
result += Pattern[rnd];
}
return result;
}
#endregion
}
/// <summary>
/// 驗證圖片類
/// </summary>
public class YZMHelper
{
#region 私有字段
private string text;
private Bitmap image;
private int letterCount = 4; //驗證碼位數
private int letterWidth = 16; //單個字體的寬度範圍
private int letterHeight = 20; //單個字體的高度範圍
private static byte[] randb = new byte[4];
private static RNGCryptoServiceProvider rand = new RNGCryptoServiceProvider();
private Font[] fonts =
{
new Font(new FontFamily("Times New Roman"),10 +Next(1),System.Drawing.FontStyle.Regular),
new Font(new FontFamily("Georgia"), 10 + Next(1),System.Drawing.FontStyle.Regular),
new Font(new FontFamily("Arial"), 10 + Next(1),System.Drawing.FontStyle.Regular),
new Font(new FontFamily("Comic Sans MS"), 10 + Next(1),System.Drawing.FontStyle.Regular)
};
#endregion
#region 公有屬性
/// <summary>
/// 驗證碼
/// </summary>
public string Text
{
get { return this.text; }
}
/// <summary>
/// 驗證碼圖片
/// </summary>
public Bitmap Image
{
get { return this.image; }
}
#endregion
#region 構造函數
public YZMHelper()
{
HttpContext.Current.Response.Expires = 0;
HttpContext.Current.Response.Buffer = true;
HttpContext.Current.Response.ExpiresAbsolute = DateTime.Now.AddSeconds(-1);
HttpContext.Current.Response.AddHeader("pragma", "no-cache");
HttpContext.Current.Response.CacheControl = "no-cache";
this.text = Rand.Number(4);
CreateImage();
}
#endregion
#region 私有方法
/// <summary>
/// 獲得下一個隨機數
/// </summary>
/// <param name="max">最大值</param>
private static int Next(int max)
{
rand.GetBytes(randb);
int value = BitConverter.ToInt32(randb, 0);
value = value % (max + 1);
if (value < 0) value = -value;
return value;
}
/// <summary>
/// 獲得下一個隨機數
/// </summary>
/// <param name="min">最小值</param>
/// <param name="max">最大值</param>
private static int Next(int min, int max)
{
int value = Next(max - min) + min;
return value;
}
#endregion
#region 公共方法
/// <summary>
/// 繪製驗證碼
/// </summary>
public void CreateImage()
{
int int_ImageWidth = this.text.Length * letterWidth;
Bitmap image = new Bitmap(int_ImageWidth, letterHeight);
Graphics g = Graphics.FromImage(image);
g.Clear(Color.White);
for (int i = 0; i < 2; i++)
{
int x1 = Next(image.Width - 1);
int x2 = Next(image.Width - 1);
int y1 = Next(image.Height - 1);
int y2 = Next(image.Height - 1);
g.DrawLine(new Pen(Color.Silver), x1, y1, x2, y2);
}
int _x = -12, _y = 0;
for (int int_index = 0; int_index < this.text.Length; int_index++)
{
_x += Next(12, 16);
_y = Next(-2, 2);
string str_char = this.text.Substring(int_index, 1);
str_char = Next(1) == 1 ? str_char.ToLower() : str_char.ToUpper();
Brush newBrush = new SolidBrush(GetRandomColor());
Point thePos = new Point(_x, _y);
g.DrawString(str_char, fonts[Next(fonts.Length - 1)], newBrush, thePos);
}
for (int i = 0; i < 10; i++)
{
int x = Next(image.Width - 1);
int y = Next(image.Height - 1);
image.SetPixel(x, y, Color.FromArgb(Next(0, 255), Next(0, 255), Next(0, 255)));
}
image = TwistImage(image, true, Next(1, 3), Next(4, 6));
g.DrawRectangle(new Pen(Color.LightGray, 1), 0, 0, int_ImageWidth - 1, (letterHeight - 1));
this.image = image;
}
/// <summary>
/// 字體隨機顏色
/// </summary>
public Color GetRandomColor()
{
Random RandomNum_First = new Random((int)DateTime.Now.Ticks);
System.Threading.Thread.Sleep(RandomNum_First.Next(50));
Random RandomNum_Sencond = new Random((int)DateTime.Now.Ticks);
int int_Red = RandomNum_First.Next(180);
int int_Green = RandomNum_Sencond.Next(180);
int int_Blue = (int_Red + int_Green > 300) ? 0 : 400 - int_Red - int_Green;
int_Blue = (int_Blue > 255) ? 255 : int_Blue;
return Color.FromArgb(int_Red, int_Green, int_Blue);
}
/// <summary>
/// 正弦曲線Wave扭曲圖片
/// </summary>
/// <param name="srcBmp">圖片路徑</param>
/// <param name="bXDir">如果扭曲則選擇爲True</param>
/// <param name="nMultValue">波形的幅度倍數，越大扭曲的程度越高,一般爲3</param>
/// <param name="dPhase">波形的起始相位,取值區間[0-2*PI)</param>
public System.Drawing.Bitmap TwistImage(Bitmap srcBmp, bool bXDir, double dMultValue, double dPhase)
{
double PI = 6.283185307179586476925286766559;
Bitmap destBmp = new Bitmap(srcBmp.Width, srcBmp.Height);
Graphics graph = Graphics.FromImage(destBmp);
graph.FillRectangle(new SolidBrush(Color.White), 0, 0, destBmp.Width, destBmp.Height);
graph.Dispose();
double dBaseAxisLen = bXDir ? (double)destBmp.Height : (double)destBmp.Width;
for (int i = 0; i < destBmp.Width; i++)
{
for (int j = 0; j < destBmp.Height; j++)
{
double dx = 0;
dx = bXDir ? (PI * (double)j) / dBaseAxisLen : (PI * (double)i) / dBaseAxisLen;
dx += dPhase;
double dy = Math.Sin(dx);
int nOldX = 0, nOldY = 0;
nOldX = bXDir ? i + (int)(dy * dMultValue) : i;
nOldY = bXDir ? j : j + (int)(dy * dMultValue);
Color color = srcBmp.GetPixel(i, j);
if (nOldX >= 0 && nOldX < destBmp.Width
&& nOldY >= 0 && nOldY < destBmp.Height)
{
destBmp.SetPixel(nOldX, nOldY, color);
}
}
}
srcBmp.Dispose();
return destBmp;
}
#endregion
}
}