Posts with exact same avatar PHOTO, but different user names…

How come there are so many posts (across many different subs) that have the EXACT SAME avatar photo, but never the same user name? I don’t mean the cartoon avatar, I mean the same exact photograph (the two I see most often are a close up white female face with dark brown hair, the other I think might be a black dog, but the pic is small and hard to see on my phone The username is always different, tho. I don’t know that much about Reddit, so forgive my ignorance, but is it a bot or someone karma farming? Should I report these posts?