scene_number.py

# image create view

if form.is_valid():
    images = Image.objects.order_by('-_id').all()
    if len(images)>0:
           # get latest image scene number
           scene_number = Images.first().scene_number + 1
    else:
          # creating first image so set scene_number =1
          scene_number = 1

    image = form.save()
    image.scene_number = scene_number

   # set image.image

   # set image.video

   # save image finally
   image.save()