Updating profile picture through serializer

Question

I cannot update a profile image on my extended user model.

Here is my serializers.py:

class UpdateUserSerializer(serializers.ModelSerializer):
    email = serializers.EmailField(required=False)
    city = serializers.CharField(source='profile.city', allow_blank=True, required=False)
    country = serializers.CharField(source='profile.country', allow_blank=True, required=False)
    profile_pic = serializers.ImageField(source='profile.profile_pic', use_url=True, required=False)

    class Meta:
        model = User
        #, 'city', 'country', 'bio'
        fields = ['username', 'email', 'password', 'first_name', 'last_name', 'city', 'country', 'profile_pic']
        # fields = UserDetailsSerializer.Meta.fields + ('city', 'country')
        extra_kwargs = {'username': {'required': False},
                        'email': {'required': False},
                        'password': {'required': False},
                        'first_name': {'required': False},
                        'last_name': {'required': False},
                        'city': {'required': False},
                        'country': {'required': False},
                        'profile_pic': {'required': False}
                        }
    def update(self, instance, validated_data):
        profile_data = validated_data.pop('profile', {})
        city = profile_data.get('city')
        country = profile_data.get('country')
        profile_pic = profile_data.get('profile_pic')

        instance = super(UpdateUserSerializer, self).update(instance, validated_data)

        profile = instance.profile
        if profile_data:
            if city:
                profile.city = city
            if country:
                profile.country = country
            if profile_pic:
                profile.profile_pic = profile.profile_pic
            profile.save()
        return instance
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When I try to update this image with a new image I do not get any error messages however the image is not updated (image remains the same).