一、驗證碼的作用

防惡意破解密碼：防止，使用程序或機器人惡意去試密碼．為了提高用戶的體驗，用戶輸入錯誤以后，才會要求輸入驗證碼．

防論壇灌水：這個是很常見的。有一種程序叫做頂帖機，如果無限制的刷，整個論壇可能到處是拉圾信息，比如，百度貼吧，你只要是新用戶或者剛剛關注的貼吧，要是發帖，會馬上出現驗證碼。
有效防止注冊：防止使用程序或機器人去無限制注冊賬號．
防刷票：網上有很多投票類的網站.
反爬：防止爬蟲爬取數據

二、原理

驗證碼于服務器端生成，發送給客戶端，并以圖像格式顯示。客戶端提交所顯示的驗證碼，客戶端接收并進行比較，若比對失敗則不能實現登錄或注冊，反之成功后跳轉相應界面。
流程
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三、如何實現

1、前期配置

1. 安裝pillow

   pip install Pillow
   

2. 安裝django-simple-captcha

   pip install  django-simple-captcha==0.5.6
   

3. 將captcha添加到setting的app中

   INSTALLED_APPS = [
       'captcha',
   ]
   

4. 添加urls.py

   urlpatterns += [
       url(r'^captcha/', include('captcha.urls')),
   ]
   

5. 配置

   # django_simple_captcha 驗證碼配置   
   # 格式  
   CAPTCHA_OUTPUT_FORMAT = u'%(text_field)s %(hidden_field)s %(image)s'  
   # 噪點樣式  
   CAPTCHA_NOISE_FUNCTIONS = ('captcha.helpers.noise_null', # 沒有樣式  
       # 'captcha.helpers.noise_arcs', # 線  
       # 'captcha.helpers.noise_dots', # 點  
   )  
   # 圖片大小  
   CAPTCHA_IMAGE_SIZE = (100, 25)  
   CAPTCHA_BACKGROUND_COLOR = '#ffffff'  
   CAPTCHA_CHALLENGE_FUNCT = 'captcha.helpers.random_char_challenge' # 圖片中的文字為隨機英文字母，如 mdsh  
   # CAPTCHA_CHALLENGE_FUNCT = 'captcha.helpers.math_challenge'    # 圖片中的文字為數字表達式，如1+2=</span>  
   CAPTCHA_LENGTH = 4 # 字符個數  
   CAPTCHA_TIMEOUT = 1 # 超時(minutes)  
   

2、示例代碼

1. forms.py

   from django import forms
   from maiziedu.models import UserProfile
   from captcha.fields import CaptchaField
   class RegisterForm(forms.Form):
       '''
       注冊
       '''
   username = forms.EmailField(widget=forms.TextInput(attrs={"placeholder": "請輸入郵箱賬號", "value": "", "required": "用戶名不能為空",}),max_length=50,error_messages={"required": "用戶名不能為空",})
    password = forms.CharField(widget=forms.PasswordInput(attrs={"placeholder": "請輸入密碼", "value": "", "required": "密碼不能為空",}),min_length=8, max_length=50,error_messages={"required": "密碼不能為空",})
       # 驗證碼
       captcha = CaptchaField()
       def clean(self):
           # 驗證碼
           try:            
               captcha_x = self.cleaned_data['captcha']            
           except Exception as e:
               raise forms.ValidationError(u"驗證碼有誤，請重新輸入")
            # 用戶名
           try:
               username=self.cleaned_data['username']
           except Exception as e:
               raise forms.ValidationError(u"注冊賬號需為郵箱格式")    
           # 登錄驗證        
           is_email_exist = UserProfile.objects.filter(email=username).exists() 
           is_username_exist = UserProfile.objects.filter(username=username).exists() 
           if is_username_exist or is_email_exist:
               raise forms.ValidationError(u"該賬號已被注冊")
           # 密碼
           try:
               password=self.cleaned_data['password']
           except Exception as e:
               raise forms.ValidationError(u"請輸入至少8位密碼");
           return self.cleaned_data 
   

2. 刷新驗證碼

   # 刷新驗證碼  
   def refresh_captcha(request):  
       verify= dict()  
       verify['cptch_key'] = CaptchaStore.generate_key()  
       verify['cptch_image'] = verify(to_json_response['cptch_key'])  
       return HttpResponse(json.dumps(verify), content_type='application/json')  
   

3. views.py

   def register(request):  
       if request.method == 'POST':  
           # 驗證碼  
           try:  
               reg_form = RegisterForm(request.POST)  
           except Exception as e:  
               # 登錄失敗 返回錯誤提示      
               err = "注冊失敗，請重試"  
               return result_response(request, err)   
           if reg_form.is_valid():  
               try:  
                   username = reg_form.cleaned_data['username']  
                   password = reg_form.cleaned_data['password']  
                   user = UserProfile.objects.create(username = username, email = username,   
                   password = make_password(password), is_active = True)  
                   user.save()  
                   # 驗證成功登錄  
                   auth.login(request, user)  
                   return result_response(request, "")  
               except Exception as e:  
                   setFormTips(reg_form, "注冊失敗，請重試")  
           else:  
               if request.POST.get('captcha_1') == "":  
                   setFormTips(reg_form, "驗證碼不能為空")   
           # 登錄失敗 返回錯誤提示      
           err = getFormTips(reg_form)  
           return result_response(request, err)   
       else:  
           reg_form = RegisterForm()  
           #  locals() 傳遞所有變量
       return render(request, 'index.html', locals())  
   

4. 刷新驗證碼

       $(function () {
               let refres_url = 'http://127.0.0.1:8000/account/verify/';
               $('.captcha').click(function () {
                   $.getJSON(refres_url, function (data) {
                       $('.captcha').attr('src', data.img_url)
                       $('#id_capt_0').val(data.haskey)
                   })
               })
           })
   

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