[joshvm]

It's a little bit more tricky than that. What the EXIF might tell you is the camera calibration parameters like focal length, distortion, perspective center, etc. That can be used to fix systematic errors in images like pincushion/barrel distortion.

To unwarp photos that were taken at odd angles you need to do some image processing. The mathematics aren't particularly difficult, it's a homography transform in most cases (rectangles). The problem is robustly detecting the page.

Dropbox has some nice write-ups on this: https://blogs.dropbox.com/tech/2016/08/fast-document-rectifi...

[zhoubear]

Thanks for the link. That blew my mind! I wish it could be added would, my phone would replace my scanner instantly.

[ikurei]

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.

[gravypod]

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.

[zhoubear]

Wow this looks awesome, thank you!

[grahamburger]

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

[nothrabannosir]

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