PhotoScan by Google Photos is an official Google app to scan pics using your Android camera. With no frills. With the right perspective. And with auto-cropping of the frames.
Using PhotoScan by Google Photos is super easy. Just place the pic you want to scan on a flat surface, focus with your device's camera, and follow the instructions on the screen. The whole process takes a few seconds.
All the pics you scan using this procedure get stored on your device memory and saved in the same folder. In any case, if the scan isn't up to scratch, just undo the changes and do the scan again.
PhotoScan by Google Photos is a super useful app to scan your hardcopy photos in seconds. The app can't do miracles, though. You need to center the image to be scanned and make sure you have good lighting if you want to get optimal results.