Apple changed iPhone images to save in HEIC format, which does not display in the Assignment grading interface.
Instructors can use a free file converter: https://www.howtogeek.com/345504/how-to-open-heic-files-on-windows-or-convert-them-to-jpeg/
Students should go to their phone's Settings > Camera > Formats, and change from high efficiency to most compatible. (This is the equivalent of saving Pages or Google Docs to Word .doc format.)
Students can also use the free Adobe Scan app to scan files to PDF. The app's logo looks like: