I use Genius Scan on my iPhone to scan documents that I need to archive (I think it's also available for Android). In addition to automatic cropping it fixes a

I use Genius Scan on my iPhone to scan documents that I need to archive (I think it's also available for Android). In addition to automatic cropping it fixes any distortions so the documents look as if they had been scanned with a flatbed scanner. It works really well for my purpose. (I have no affiliation with them, just love the app)