The new photos app allows you to choose photos and videos from your device (local and online)
Google photos app is the next version of the gallery app, which is an integral part of the Google Plus app. This app allows other apps to browse/edit/share/choose images and videos (both local and online). It's an alternate application for the default Gallery app.
Reference: https://support.google.com/plus/answer/3453521?hl=en