No one is telling you to respond to every ass-hat. If you are taking it that way, you still don't get it and this will be my last reply to you on the matter. I am telling people to think critically using well-documented stories and information on this forum.
You very much believed a flawed analogy. It isn't hard to verify the owner or landlord of a house. It is clearly shown and proven in public record deeds.
Images, ownership, and the copyright registration matter are not so clear. There is uncertainty. And you are not receiving a letter from a Nigerian scammer. You are receiving a letter from a well-known media company who is also known for sending these legal demand letters.
If you choose not to respond because it was a de-minimus or severe infringement, that is one thing. But it makes no sense to me to not respond if you think you are clearly in the right. If you don't mind getting the ongoing letters and the remote possibility of a lawsuit, then you can stay silent and NOT explain it. To me, it costs very little to write an informed letter vs. staying in the dark.
Having said all that, everyone's case is their own. But expect to be notified periodically for the next 3 years. For some, it's no biggie. For others, it is a mental distraction and cloud over them for a long period of time.
None of us have a dog in your fight with Getty. But many of us happen to be very experienced at this sort of stuff of pushing back and defending one's self.
And why I waited so long to respond: Maybe my reasoning is flawed, but a poster used the analogy on this forum of owning a house and receiving a letter for rent due from someone claiming they own your house. Do you really need to respond to every ass-hat claiming you owe them rent on something that is blatantly false? Apparently yes....