Show image as thumbnail in Django admin change list (list view) and change form

omega.py

# Django 3.2.15 LTS

# Project structure
#
# project/
#    config/
#        __init__.py
#        settings.py
#        urls.py
#        asgi.py
#        wsgi.py
#    core/
#        __init__.py
#        admin.py
#        apps.py
#        models.py
#        tests.py
#        urls.py
#        views.py
#        templates/
#            core/
#                my_widget.html
#        migrations/
#    manage.py

################
# core/models.py
################

class Profile(models.Model):
    email = models.EmailField()
    avatar = models.ImageField(upload_to="media")

####################
# config/settings.py
####################

MEDIA_URL = "/media/"
MEDIA_ROOT = BASE_DIR

################
# config/urls.py
################

from django.conf import settings
from django.conf.urls.static import static

if settings.DEBUG:
    urlpatterns += static(settings.MEDIA_URL, document_root=settings.MEDIA_ROOT)

###############
# core/admin.py
###############

@admin.register(Profile)
class ProfileAdmin(admin.ModelAdmin):
    # Show image in change list (list view)
    list_display = ("email", "show_avatar")
    # Show image in add/change form as a readonly field
    readonly_fields = ("show_avatar",)

    # Customize image upload widget to show uploaded image as a thumbnail
    def get_form(self, request, obj=None, **kwargs):
        form = super().get_form(request, obj, **kwargs)
        form.base_fields["avatar"].widget.template_name = "core/my_widget.html"
        return form 
    
    # Calculated field
    def show_avatar(self, obj):
        from django.utils.html import format_html

        return format_html('<img width=70 height=70 src="{}" />', obj.avatar.url)
    
    # Column name
    show_avatar.short_description = "Thumbnail"

####################################
# core/templates/core/my_widget.html
####################################

<p class="file-upload">
  Currently: 
  <img width=70 height=70 src="/media/{{ widget.value }}" />
  <br>
  Change:
  <input type="file" name="avatar" accept="image/*" id="id_avatar">
</p>