[Sync] Image update: do not compile unchanged images

utils/Sync/sync/models/__init__.py

@@ -1,3 +1,12 @@
+def find(store, item_id: str):
+    q = {'id': item_id}
+    try:
+        return store.find_one(q)
+    except ValueError:
+        pass
+    return None
+
+
 class Model:
     def __init__(self, provider, store, file):
         super().__init__()
@@ -19,7 +28,17 @@ class Model:
         return None
 
     async def is_changed(self):
-        return False
+        i = find(self.store, self.id)
+        return self._is_changed_hash(i)
+
+    def _is_changed_hash(self, item):
+        if not item:
+            return True
+
+        if 'hash' not in item:
+            return True
+
+        return not (self.hash == item['hash'])
 
     async def save(self):
         pass