Django queryset grouped by count of values in Postgres JSONField

My model:

from django.contrib.postgres.fields import JSONField

class Image(models.Model):
    tags = JSONField(null=False, blank=True, default={})

tags field value can be empty, or something like:

[
   {"tag": "xxx"}, 
   {"tag": "yyy"},
   {"tag": "zzz"}
]

The number or dicts may vary (from 0 to N).

I need to make a query that counts Images grouped by number of tags. Something like:

{
   "0": "345",
   "1": "1223",
   "2": "220",
   ...
   "N": "23"
}

where the key is the number of tags, and the value is the count of Image objects that contains this number of tags.

How can i do that? Thank you for your help!

UPDATE

I modified my code: now I don't use JsonField, but a dedicated model:

class ImageTag(models.Model):
    image = models.ForeignKey(Image)
    tag = models.CharField()

The question is the same :)