When editing the description of a cohort with the HTML editor, it is not possible to upload images or media.
This may be because of the context not being set for cohorts (or being set to zero), so there is no temporary editing area for attached files.
- Log in as admin
- Navigate to Site Administration -> Users -> Accounts -> Cohorts
- Click on the "Insert/edit image" button or the "Moodle media" button.