add custom image model, fetch alt text

dnscms/venues/models.py

@@ -22,7 +22,7 @@ class VenuePage(Page):
     show_in_menus = False
 
     featured_image = models.ForeignKey(
-        "wagtailimages.Image",
+        "images.CustomImage",
         null=True,
         blank=True,
         on_delete=models.SET_NULL,