Over the last week or so, I have come across several links that have described this story. What I find amazing is that the legal community has not done a case study on this. It appears that Prince has very carefully threaded a set of legal needles in order to do this. That and along with having a very talented and capable legal firm to defend his approach (with an equally large checkbook to boot). The folks whose material is being used, understandably are less than aggressive, because they really can't afford to run up an a hefty legal bill over essentially a throwaway image that they posted on Instagram.
I am guessing that the Prince and his lawyer have not really had their legal position stressed to any extreme. I am surprised with the outcome from the appeals court overturn and agreeing with Prince. That will just deter anyone else from complaining.