I had some faculty interested in allowing students to scan and submit handwritten work to their online courses. Creating a Canvas assignment that only accepts JPG pictures that students take with their phones wasn't good enough because instructors can't use the SpeedGrader (DocViewer) to annotate student work. [Update: as of the June 2, 2018 Canvas release, you can annotate images in DocViewer now. There still may be some advantages to converting scanned images to a single PDF, however.]
So the solution we have now is for students to use one app on their phone to convert photos of their work to a PDF document and then submit that PDF to Canvas via the Canvas Student app. One popular app for creating PDF scans in CamScanner, but perhaps other scanner apps would work well, too, such as Tiny Scanner. I know many have already known about this solution for years now, but I couldn't see it documented anywhere on this site.
Luckily, someone already made video instructions for this workflow on both Android and iOS devices. I would also though recommend students turn their phone sideways, so that the images in the PDFs aren't rotated incorrectly in the SpeedGrader (which doesn't have a button to rotate documents or images back to the correct orientation - vote for the feature here).
FlipGrid - Video Discussion Option
Another alternative technique that is growing in popularity is to let students use FlipGrid to submit videos in which they describe and comment on their work. See