title: django ImageField empty after form post
body: <p>When I upload a photo to django through form the image field is empty. I confirmed this by using <code>logging.info(form.cleaned_data['picture'] )</code></p>
  
  <p>I checked through the console that the form has <code>'multipart/form-data'</code></p>
  
  <p>The model :</p>
  
  <pre><code>class Person(models.Model):
      user = models.ForeignKey(User, default=1)
      name = models.CharField(max_length=250,null=True)
      last_name = models.CharField(max_length=500)        
      treatment_plan=models.CharField(max_length=256,null=True,blank=True)
      treatment_done=models.CharField(max_length=256,null=True,blank=True)        
  
      picture = models.ImageField(upload_to='image', storage=DEFAULT_FILE_STORAGE,blank=True)
  
      def __str__(self):
          return self.name
  </code></pre>
  
  <p>the modelForm :</p>
  
  <pre><code>class PersonForm(forms.ModelForm):
  
      class Meta:
          model = Person
          fields = ['name', 'last_name', 'age', 'martial_status', 'mobile', 'sex',
                    'amount_paid','amount_left','note', 'address','date','picture','treatment_done','treatment_plan','chief_complain']
          widgets = {
              'name': forms.TextInput(attrs={'required': True, 'class': 'form-control',
                                               'placeholder': 'name'}),
              'last_name': forms.TextInput(attrs={'required': True, 'class': 'form-control',
              'picture': forms.FileInput(attrs={'required': False,'class': 'form-control','enctype': 'multipart/form-data'}),
  </code></pre>
  
  <p>view.py :</p>
  
  <pre><code>def add_person(request):
      if not request.user.is_authenticated():
          return render(request, 'core/login.html')
      else: 
          form = PersonForm(request.POST or None,request.FILES or None,instance=Person())
          #form = PersonForm(request.POST or None,request.FILES )
          if form.is_valid():
  
              persons = form.save()
  
              persons.user = request.user
              #to capitalized the first letter so we have consistency when querying , this is a workaround since __iexact is not working
              persons.name=persons.name.title()
              persons.last_name=persons.last_name.title()
              logging.info(form.cleaned_data['last_name'] )
  
              persons.save()
  
              return redirect('home')
          context = {
              "form": form,
          }
          return render(request, 'core/add_person.html', context)
  </code></pre>
  
  <p>The html template :</p>
  
  <pre><code>&lt;div class="col-sm-4 form-group"&gt;
     &lt;label for="address"&gt;{% trans "Address" %}&lt;/label&gt;
     {{ form.address|add_class:"form-control" }}
    &lt;/div&gt;
        &lt;div class="col-sm-4 form-group"&gt;
     &lt;label for="pic"&gt;{% trans "Picture" %}&lt;/label&gt;
      {{form.picture}}
    &lt;/div&gt;
  </code></pre>