For courses with many related lessons, my clients use the same general thumbnail across categories and lessons. It would save so much time to select a previously uploaded thumbnail and apply it to other categories and lessons. Ideally we could select a thumbnail at the category level and have an option to use it as the default thumbnail for all lessons in that category and then we could just replace any individual ones as needed. I would think it also makes sense to just be able to upload all of the thumbnails to the media storage and access them from there, but I assume that's a database issue with memberships vs. the rest of the tools in HL.