I'm an Android user. What's a good app to use as a separate photo gallery?

I'm an avid roleplayer on Twitter, and because of this my gallery is usually cluttered with pictures of the characters I use. It's very embarrassing to scroll through my gallery in public.

My phone has a fingerprint-protected "vault" to hide pics I don't want anyone to see, but if I want to post those pics, I have to manually go into my vault, select the picture(s) I want to use, restore them to my regular gallery, post them, and then move them back to the vault again. It's very tedious.

So in essence I'm looking for a photo gallery app that I can dump all my character pics in, but also one that lets me post them directly from Twitter's image selector as normal. Then I'll be able to use my default gallery in peace.