Here’s a Microsoft Office app that helps you capture the entire document or whiteboard. It even compensates for keystone effects (if you’re not able to square up the picture, the app will automatically square things up for you!). It’s free — and it works. See it for iPhone at…

https://itunes.apple.com/us/app/office-lens/id975925059?mt=8

and Android at…

https://play.google.com/store/apps/details?id=com.microsoft.office.officelens&hl=en_US

(Thanks Kent!)