It's just an educated guess, so I don't know.

Besides, such company would do its best to stay discrete, by design.

I'm aware of one such company that uses Imgur like that and that deals with celebs. Imgur isn't their primary target, it's just a handy layer of abstraction away from the real target so the content can't TRULY be taken down on the target site. Plus, it shows you how many impressions you get for free. That way they can gather up their campaign image urls and views at the end of the contract and show hard results without the need for a fancy, paid analytics dashboard or campaign tracking system.