验证码功能一般是用于防止批量注册的，不少网站为了防止用户利用机器人自动注册、登录、灌水，都采用了验证码技术。所谓验证码，就是将一串随机产生的数字或字母或符号或文字，生成一幅图片， 图片里加上一些干扰象素（防止OCR），由用户肉眼识别其中的验证码信息，输入表单提交网站验证，验证成功后才能使用某项功能。
常见的验证码有如下几种：
1、纯数字验证码，一般为四位随机数字；
2、数字+字母验证码，一般从数字（0~9）和字母(A~Z和a~z)中随机抽出几个字符组成；
3、汉字验证码，相对而言，这种验证码比较少见一点，实现起来也相对复杂一些，但在不少网站中还是可以看到的；
一、纯数字验证码的实现
（1）使用随机数方式，代码如下：
View Code 1 view plaincopy to clipboardprint? 2 private String GetRandomint(int codeCount) 3 { 4 Random random = new Random(); 5 string min = ""; 6 string max = ""; 7 for (int i = 0; i < codeCount; i++) 8 { 9 min +="1"; 10 max+="9"; 11 } 12 return (random.Next(Convert.ToInt32(min),Convert.ToInt32(max)).ToString()); 13 } 14 private String GetRandomint(int codeCount) 15 { 16 Random random = new Random(); 17 string min = ""; 18 string max = ""; 19 for (int i = 0; i < codeCount; i++) 20 { 21 min +="1"; 22 max+="9"; 23 } 24 return (random.Next(Convert.ToInt32(min),Convert.ToInt32(max)).ToString()); 25 } (2)使用随机组合方式，代码如下
View Code 1 view plaincopy to clipboardprint? 2 private string CreateRandomCode(int codeCount) 3 { 4 string allChar = "0,1,2,3,4,5,6,7,8,9"; 5 string[] allCharArray = allChar.Split(','); 6 string randomCode = ""; 7 int temp = -1; 8 Random rand = new Random(); 9 for (int i = 0; i < codeCount; i++) 10 { 11 if (temp != -1) 12 { 13 rand = new Random(i * temp * ((int)DateTime.Now.Ticks)); 14 } 15 int t = rand.Next(9); 16 if (temp == t) 17 { 18 return CreateRandomCode(codeCount); 19 } 20 temp = t; 21 randomCode += allCharArray[t]; 22 } 23 return randomCode; 24 } 25 private string CreateRandomCode(int codeCount) 26 { 27 string allChar = "0,1,2,3,4,5,6,7,8,9"; 28 string[] allCharArray = allChar.Split(','); 29 string randomCode = ""; 30 int temp = -1; 31 Random rand = new Random(); 32 for (int i = 0; i < codeCount; i++) 33 { 34 if (temp != -1) 35 { 36 rand = new Random(i * temp * ((int)DateTime.Now.Ticks)); 37 } 38 int t = rand.Next(9); 39 if (temp == t) 40 { 41 return CreateRandomCode(codeCount); 42 } 43 temp = t; 44 randomCode += allCharArray[t]; 45 } 46 return randomCode; 47 } 2、数字+字母验证码的实现
View Code 1 view plaincopy to clipboardprint? 2 private string CreateRandomCode(int codeCount) 3 { 4 string allChar = "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,W,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"; 5 string[] allCharArray = allChar.Split(','); 6 string randomCode = ""; 7 int temp = -1; 8 Random rand = new Random(); 9 for (int i = 0; i < codeCount; i++) 10 { 11 if (temp != -1) 12 { 13 rand = new Random(i * temp * ((int)DateTime.Now.Ticks)); 14 } 15 int t = rand.Next(61); 16 if (temp == t) 17 { 18 return CreateRandomCode(codeCount); 19 } 20 temp = t; 21 randomCode += allCharArray[t]; 22 } 23 return randomCode; 24 } 25 private string CreateRandomCode(int codeCount) 26 { 27 string allChar = "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,W,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"; 28 string[] allCharArray = allChar.Split(','); 29 string randomCode = ""; 30 int temp = -1; 31 Random rand = new Random(); 32 for (int i = 0; i < codeCount; i++) 33 { 34 if (temp != -1) 35 { 36 rand = new Random(i * temp * ((int)DateTime.Now.Ticks)); 37 } 38 int t = rand.Next(61); 39 if (temp == t) 40 { 41 return CreateRandomCode(codeCount); 42 } 43 temp = t; 44 randomCode += allCharArray[t]; 45 } 46 return randomCode; 47 } 48