some information about "INCLUDED IN MEMBERSHIP" requested...

I recently discovered that some of my Images are marked as "INCLUDED IN MEMBERSHIP". You can see that when the photographs are underlined with an orange bottom border. How did it get there? Does this inclusion happen per chance or does it say something about inferior/superior image quality? Just curious. Maybe someone can clear that up for me, please.
What about the payment of such assets. Are they sold for the same price or only for cheap?