I typically will store the picture in my camera roll, unless it is something to store for the future, in which case I will store it in Evernote - which is an amazing site to store all your notes across all devices. I will post about Evernote in the future (as you can now search Google Drive files in Evernote).
I used the scannable app many times for parents when they needed a file to print out because their child lost it. I would scan the document with Scannable, save it to my camera roll, attach it in an e-mail, and they would sign and return it the same day. It basically took having to go to the copier and scan it.
Below is a screenshot of what Scannable will look like when you use it.