The Photos app is a Universal (Metro) app which comes pre-installed in Windows 10. It is a Store app which is intended to replace Windows Photo Viewer, since Microsoft wants to make the whole user environment look and work the same on Windows 10 Mobile and Windows 10 for PCs. However, interested users can restore the classic desktop app, Windows Photo Viewer. With recent updates, you can mark an image as a favorite. The Photos app will create a new "Favorites" album for you.