For LifterLMS 3.0 and higher:
Utilize LifterLMS Labs: Action Manager and check the box in the lab’s settings for “Featured Image” under “Single Course Actions”
For LifterLMS 2.7 and lower:
If your theme natively supports featured images for custom post types you likely will see duplicate featured images on a course.
To resolve this issue you can disable LifterLMS course banners. We created a function to add banners for themes which don’t add a featured image automatically.
Navigate to LifterLMS -> Settings -> Courses and locate the checkboxes for “Course Display” and then uncheck the box next to “Display featured image as course banner.”
Save the settings and the duplicate image will be removed.