Installation

pip3 install wagtail-snippet-image

How use it

from django.db.models import (
    CharField,
    ForeignKey,
    SET_NULL,
    CASCADE,
)
from wagtail_snippet_image import SnippetImageField
from wagtail.core.models import Page
from wagtail.admin.edit_handlers import FieldPanel
from wagtail.images.edit_handlers import ImageChooserPanel
from modelcluster.fields import ParentalKey
from modelcluster.contrib.taggit import ClusterTaggableManager
from taggit.models import TaggedItemBase


class PageTag(TaggedItemBase):
    content_object = ParentalKey(
        'home.HomePage',
        on_delete=CASCADE,
        related_name='tagged_items',
    )


class Statuses:
    DRAFT = 'draft'
    PUBLISH = 'publish'

    CHOICES = (
        (DRAFT, 'Draft'),
        (PUBLISH, 'Publish'),
    )


class HomePage(Page):
    background = ForeignKey(
        'wagtailimages.Image',
        verbose_name='Изображение для обложки',
        related_name='cover_images',
        on_delete=SET_NULL,
        blank=True,
        null=True,
    )

    snippet_image_field = SnippetImageField(
        verbose_name='Example snippet image field',
        null=True,
    )

    status = CharField(
        max_length=20,
        choices=Statuses.CHOICES,
        default=Statuses.DRAFT,
    )

    tags = ClusterTaggableManager(through=PageTag, blank=True)

    content_panels = Page.content_panels + [
        ImageChooserPanel('background'),
        ImageChooserPanel('snippet_image_field'),
        FieldPanel('status'),
        FieldPanel('tags'),
    ]

    def get_snippet_image_background(self, snippet_type):
        return self.background and self.background.file and self.background.file.path \
            if snippet_type == 'default' else None

    def get_snippet_image_center(self, snippet_type):
        return (self.background.focal_point_x, self.background.focal_point_y) \
            if snippet_type == 'default' and self.background \
               and self.background.focal_point_x and self.background.focal_point_y \
            else None

    def get_snippet_image_text(self, snippet_type):
        return self.title if snippet_type == 'default' else None

    def snippet_image_should_be_created(self):
        return self.status == Statuses.PUBLISH

    # Wagtail custom methods for create wagtail images for sharing snippet image
    def get_snippet_image_title(self, snippet_type):
        return self.title if snippet_type == 'default' else None

    def get_snippet_image_tags(self, snippet_type):
        return self.tags.names() if snippet_type == 'default' else None

And use it in template:

<meta property="og:image" content="{{ image(page.snippet_image_field, 'original') }}" />

Read more in home.