Actually store the generated image storage in the database, and allow it to be garbage collected when the parent image storage is collected.

data/database.py

@@ -192,7 +192,6 @@ class PermissionPrototype(BaseModel):
     )
 
 
-
 class AccessToken(BaseModel):
   friendly_name = CharField(null=True)
   code = CharField(default=random_string_generator(length=64), unique=True,
@@ -238,6 +237,23 @@ class ImageStorage(BaseModel):
   uploading = BooleanField(default=True, null=True)
 
 
+class ImageStorageTransformation(BaseModel):
+  name = CharField(index=True, unique=True)
+
+
+class DerivedImageStorage(BaseModel):
+  source = ForeignKeyField(ImageStorage, null=True, related_name='source')
+  derivative = ForeignKeyField(ImageStorage, related_name='derivative')
+  transformation = ForeignKeyField(ImageStorageTransformation)
+
+  class Meta:
+    database = db
+    read_slaves = (read_slave,)
+    indexes = (
+      (('source', 'transformation'), True),
+    )
+
+
 class ImageStorageLocation(BaseModel):
   name = CharField(unique=True, index=True)
 
@@ -422,4 +438,4 @@ all_models = [User, Repository, Image, AccessToken, Role, RepositoryPermission,
               OAuthApplication, OAuthAuthorizationCode, OAuthAccessToken, NotificationKind,
               Notification, ImageStorageLocation, ImageStoragePlacement,
               ExternalNotificationEvent, ExternalNotificationMethod, RepositoryNotification,
-              RepositoryAuthorizedEmail]
+              RepositoryAuthorizedEmail, ImageStorageTransformation, DerivedImageStorage]