diff -u b/image_approval.module b/image_approval.module
--- b/image_approval.module
+++ b/image_approval.module
@@ -156,7 +156,9 @@
     unset($values['picture_upload']);
     image_approval_save_upload_file($temp_image);
     drupal_set_message(t('Your image is sent for moderation, will be uploaded once approved.'), 'warning');
-    rules_invoke_event('user_image_submitted_for_moderation', $form_state['user']);
+    if (module_exists('rules')) {
+      rules_invoke_event('user_image_submitted_for_moderation', $form_state['user']);
+    }
   }
 }