Earlier quoted context omitted.
Lots of people ironically put the Getty watermark on pictures and memes that they make to satirically imply that they are pulling stock photos off the internet with the printscreen function instead of paying for them.
Memes generally would not fall under the category of non-copyrighted material; they’re most of the time extremely copyrighted material just being used without permission. And even a wholly original work an artist sarcastically puts a Getty watermark and then licensed under Creative Commons or something would fall into very murky territory – the Getty watermark itself is the intellectual property of Getty. The origina…
I agree with you that it is also possible that people posted Getty thumbnails to some sites as though they are public domain, and that is how the AIs learned the watermark.