Wagtail Forms - Upload Image Field - Extend AbstractFormField Class

models.py

from wagtail.wagtailforms.models import AbstractFormField, FORM_FIELD_CHOICES
class FormField(AbstractFormField):
    FORM_FIELD_CHOICES = list(FORM_FIELD_CHOICES) + [('image', 'Upload Image')]
    field_type = models.CharField(
        verbose_name=_('field type'),
        max_length=16,
        choices=FORM_FIELD_CHOICES)
    page = ParentalKey('FormPage', related_name='form_fields')