Since others are commenting alternative apps, I'll chime in:

https://www.camscanner.com/

I've been using CamScanner on Android since forever. I only stopped a few months ago because I moved to iOS (and didn't realize it's also there).

It does the page detection fairly well, but also let's you correct it. Very useful, specially when the picture is bad. I then used to upload it to Dropbox.

Also see this for more implementation details: https://www.pyimagesearch.com/2014/09/01/build-kick-ass-mobi...

This could be done server side if you're already doing ocr.

Google Drive mobile app does this natively (at least on Android) there's a 'Scan' option when adding a file that will do it.

Scannable (by Evernote ) does this wonderfully. Allows exporting as pdf and storing wherever. I’m a fan.