Database for milions of photos?

What database system should i choose for millions of photos? I need to do it for my company where i work. Those are private photos, security involved. No 3rd party hosting cloud storage is allowed. I have large nas system for storing, but need to write an app in C# to manage it. So what system should i use - Oracle / Firebird / PostgreSQL, sqlite? Which is the best? Also i probably will have to use data encryption. I prefer free/ open source /gpl or other free license type system, so no ms sql server.

Thanks.