by Mark Pearson.
Nate,
Try backing up a course with user data and restoring to a temp course in a test category. Then unenrol all the users. I wonder whether the images are associated with the teacher user account?
If you have Legacy Course Files enabled but hidden the images should come over from 1.9 courses (at least that's my expereince), but losing them from a 2.3 install course backup is very strange.
Let us know how you get on.
Mark