原理：hash_key和用户输入的验证码发送到数据库作联合查询
1.在项目虚拟环境中安装captcha
pip install django-simple-captcha ==0.4.6
2.在setting中设置
INSTALLED_APPS = ['captcha',]
3.在url中进行设置
url(r'^captcha/', include('captcha.urls')),
4.生成注册表
python manage.py makemigrations
python manage.py migrate
5.创建forms.py文件，编写相关函数
导入from captcha.fields import CaptchaField
class RegisterForm(forms.Form):
email = forms.EmailField(required=True)
password = forms.CharField(required=True, min_length=5)
captcha = CaptchaField()
设置中文显示：captcha = CaptchaField(error_messages={"invalid": u"验证码错误"})
6.在views函数中实例化并传入到html页面
{{ register_form.captche }}
