Omit a gallery from getting indexed by Solr

There is not a way to fully exclude a media gallery from the search index but the search index will honor permissions if its possible to limit access using permissions/roles.

You could try to remove the entries in the SearchIndexing.AfterBulkIndex using Apis.Get<ISearchResult>().Delete but I have had some issues with this in the past where the delete didn't actually remove it from solr 

community.telligent.com/.../searchresults-in-process-api-service

In our last community admins had an option to 'hide this content from search'. This prevented the item being picked up either by search and also being exposed/highlighted on any 'recent activity' feeds. 

It was really useful especially for contentious forum threads that you didn't want to keep getting bumped up and highlighted to all users in the activity feeds or bumped back up to the top of the forum threads list every time someone posted a reply. 

Again it's something that we found incredibly useful and really miss from the OOTB Verint offering.