Everyone impacted by Nick Youngson claims really should read and understand the Memorandum of Law filed by Meyer, Suozzi, English & Klein, P.C. in their case against Higbee and Youngson. Essentially it boils down to whether the attribution requirement of the Creative Commons license was a covenant (a term of the contract that would allow Youngson to sue for breach of contract and damages, but not copyright violation) or a condition (failing to attribute means that the license was invalid, and thus allowing Youngson to bring a copyright violation claim). The Youngson websites "mysteriously" changed for many images this summer to add language stating that attribution is a CONDITION, highlighting (IMO) that previously it was a covenant. Because most people make zero dollars off their images, they have no damages to sue under the covenant/breach of contract claim. Youngson also conveniently scrubbed the websites off the wayback machine around the same time, likely to hide the fact that it previously stated it was just "required" = covenant. Luckily we were able to capture an image before they did this, so we have pictures of the "before" and "after" showing how they changed the language on the website to try to retroactively make attribution a condition. I think that Youngson/Higbee realized they messed up, and so added the language to make their honeypot more effective. But what that means is that everyone caught up in this scam prior to the website being edited MAY have a strong argument that there was only a failed covenant of the license (which basically means no $ for Youngson/Higbee), but no basis for a copyright violation claim (where the big bucks are). Everyone getting letters from them should obviously consult an attorney in their jurisdiction, but I think the MOL is a useful read.
https://cases.justia.com/federal/district-courts/new-york/nyedce/2:2018cv03353/418211/11/0.pdf