title: EmployeeFilterSet resolved field 'emp_photo' with 'exact' lookup to an unrecognized field type ImageField
body: <p>I am trying to set up django filter but keep seeing an error message as shown below</p>
  
  <blockquote>
    <p>EmployeeFilterSet resolved field 'emp_photo' with 'exact' lookup to an unrecognized field type ImageField. Try adding an override to 'Meta.filter_overrides'. See: <a href="https://django-filter.readthedocs.io/en/master/ref/filterset.html#customise-filter-generation-with-filter-overrides" rel="nofollow noreferrer">https://django-filter.readthedocs.io/en/master/ref/filterset.html#customise-filter-generation-with-filter-overrides</a></p>
  </blockquote>
  
  <p>To the best of my knowledge, I followed the docs <a href="https://django-filter.readthedocs.io/en/master/guide/usage.html#overriding-default-filters" rel="nofollow noreferrer">as seen here</a>. </p>
  
  <p>My models:</p>
  
  <pre><code>from __future__ import unicode_literals
  import django_filters
  from django.core.validators import RegexValidator
  from django.db import models
  from django.utils.encoding import python_2_unicode_compatible
  from django.utils.translation import ugettext_lazy as _
  
  @python_2_unicode_compatible
  class Employee(models.Model):
      # basic information of employee
      first_name = models.CharField(_('first name'), max_length=40)
      last_name = models.CharField(_('last name'), max_length=40)
      emp_photo = models.ImageField(_('passport'))
      date_of_birth = models.DateField(_('birthday'))
      gender = models.CharField(_('gender'), max_length=15, choices=GENDER_CHOICES, default=['MALE', 'Male'])
      house_address = models.CharField(_('house address'), max_length=50)
      city_of_residence = models.CharField(_('city'), max_length=40)
      state_of_residence = models.CharField(_('state'), max_length=40, choices=NIGERIAN_STATE_CHOICES)
      country_of_residence = models.CharField(_('country'), max_length=40, choices=COUNTRY_CHOICES,
                                              default=[156, 'Nigeria'])
      state_of_origin = models.CharField(_('state of origin'), max_length=40, choices=NIGERIAN_STATE_CHOICES)
      local_govt_of_origin = models.CharField(_('LGA of origin'), max_length=40)
      town_or_city_of_origin = models.CharField(_('town or city'), max_length=40)
      nationality = models.CharField(_('nationality'), max_length=40, choices=COUNTRY_CHOICES, default=[156, 'Nigeria'])
      email = models.EmailField(_("email address"))
      phone_regex = RegexValidator(regex=r'^\+?1?\d{9,15}$',
                                   message="phone number must be entered in the "
                                           "format: '+2340000000000'. Up to 15 digits allowed.")
      phone_number = models.CharField(_('phone number'), validators=[phone_regex], max_length=17, blank=True)
  
     # employment record of employee
      emp_id = models.IntegerField(unique=True, primary_key=True, default=1)
      job_title = models.CharField(_('job title'), max_length=50)
      dept_name = models.CharField(_('department name'), max_length=50)
      branch_name = models.CharField(_('branch name'), max_length=50)
      hire_date = models.DateField(_('hire date'))
  
      class Meta:
          verbose_name = _('Employee')
          verbose_name_plural = _('Employees')
  
      def __str__(self):
          return "{} {}".format(self.first_name, self.last_name)
  
  class EmployeeFilter(django_filters.FilterSet):
      first_name = django_filters.CharFilter(method='custom_filter')
  
      class Meta:
          model = Employee
          exclude = ['emp_photo']
          fields = ['first_name', 'last_name', 'branch_name']
  
      def custom_filter(self, queryset, value, first_name=None):
          return queryset.filter(**{
              first_name: value,
          })
  </code></pre>
  
  <p>Tables:</p>
  
  <pre><code>import django_tables2 as tables
  
  from .models import Employee
  
  class EmployeeTable(tables.Table):
  
      class Meta:
          model = Employee
          template_name = "django_tables2/bootstrap-responsive.html"
          fields = ("emp_id", "first_name", "last_name", "job_title", "dept_name", "hire_date")
          export_formats = ['csv', 'xlsx']
  </code></pre>
  
  <p>Views:</p>
  
  <pre><code>from django.contrib.auth.decorators import login_required
  from django.shortcuts import render
  from django_tables2 import RequestConfig
  from django_tables2.export import TableExport
  
  from .models import Employee
  from .models import EmployeeFilter
  from .tables import EmployeeTable
  
  
  @login_required()
  def employees(request):
      filter = EmployeeFilter(request.GET, queryset=Employee.objects.all())
      table = EmployeeTable(filter.qs)
      RequestConfig(request).configure(table)
  
      export_format = request.GET.get("_export", None)
  
      if TableExport.is_valid_format(export_format):
          exporter = TableExport(export_format, table)
          return exporter.response("table.{}".format("csv", "xlsx"))
  
      return render(request, "employees/employees.html", {
          "table": table,
          "filter": filter
      })
  </code></pre>
  
  <p>Template:</p>
  
  <pre><code> &lt;!--Employees data--&gt;
              &lt;div class="filter-container container-fluid"&gt;
                  &lt;div class="row"&gt;
                      &lt;div class="col-md-10"&gt;
                          &lt;!--filter form--&gt;
                          &lt;form action="" class="form form-inline employee-search-form" method="get"&gt;
                              {% bootstrap_form filter.form layout='inline' %}
                              {% bootstrap_button 'filter' %}
                          &lt;/form&gt;
                      &lt;/div&gt;
  
                      &lt;div class="col-md-2"&gt;
                          &lt;div class="btn-group download-btn"&gt;
                              &lt;button aria-expanded="false" aria-haspopup="true"
                                      class="btn btn-warning dropdown-toggle"
                                      data-toggle="dropdown" type="button"&gt;
                                  Download
                              &lt;/button&gt;
                              &lt;div class="dropdown-menu"&gt;
                                  &lt;a class="dropdown-item" href="{% querystring '_export'='csv' %}"&gt;csv&lt;/a&gt;
                                  &lt;a class="dropdown-item" href="{% querystring '_export'='xlsx' %}"&gt;xlsx&lt;/a&gt;
                              &lt;/div&gt;
                          &lt;/div&gt;
                      &lt;/div&gt;
                  &lt;/div&gt;
              &lt;/div&gt;
              &lt;!-- data rendered here --&gt;
              {% render_table table 'django_tables2/bootstrap.html' %}
          &lt;/div&gt;
  </code></pre>
  
  <p>Error message:
  <a href="https://i.stack.imgur.com/LiGgi.png" rel="nofollow noreferrer"><img src="https://i.stack.imgur.com/LiGgi.png" alt="error image"></a></p>
  
  <p>I will very much appreciate if someone can help me out.</p>