How to query Android MediaStore Content Provider, avoiding orphaned images?

I'm trying to provide an in-app Activity which displays thumbnails of photos in the device's media store, and allow the user to select one. After the user makes a selection, the application reads the original full-size image and does things with it.

Android. Content provider or Database?

Since I've seen a presentation from Google IO I'm a bit confused in the question, if it's better to use content providers or databases. Or it makes no difference if I don't want to share any data with other applications.