Bad assumption on my part...

... Seeing the name and the module, figured this schema was just
misplaced... Appears that the `islandora_image` thing is indeed in
`islandora` proper.

config/schema/islandora.schema.yml

@@ -166,6 +166,10 @@ condition.plugin.node_had_namespace:
     pid_field:
       type: ignore
       label: 'PID field'
+      
+field.formatter.settings.islandora_image:
+  type: field.formatter.settings.image
+  label: 'Islandora image field display format settings'
 
 condition.plugin.islandora_entity_bundle:
   type: condition.plugin

modules/islandora_image/config/schema/islandora_image.schema.yml

@@ -29,7 +29,3 @@ action.configuration.generate_image_derivative:
     path:
       type: text
       label: 'File path with extension'
-
-field.formatter.settings.islandora_image:
-  type: field.formatter.settings.image
-  label: 'Islandora image field display format settings'