Photoscan by Google Photos is a great standalone photo scanning app.
Hold your phone over a photo, aim your camera, and the app basically does the rest. It crops, rotates and makes color corrections of your scanned photo.
You can then save it as a file in your phone or the cloud or share it with others. The app is free for iOS and Android.
Photo Scanner Plus scans multiple analog photographs in a single shot. This feature lets you quickly convert large volumes of old photos.
The app auto-detects picture boundaries, auto-rotates sideway pics, crops and saves to digital photo albums.
The app Pic Scanner also allows for scanning multiple photos at a time.
Features include fully automatic cropping, photo editing tools and filters to give old photos a new look. Add captions to type in dates, places and names.
As a bonus, no ads, watermarks or subscription sign-ups are required. The app is 2-99 for iOS.