Data Poisoning could be a tool we use to identify AI that has used copyritten material, or we use it to mess with AI.
https://www.vice.com/en/article/infinite-ai-homer-simpson-cover-songs-poisoned-soulseek/
https://mosis.eecs.utk.edu/harmonycloak.html
https://mosis.eecs.utk.edu/publications/meerza2024harmonycloak.pdf
People have actually been doing this to catch plagiarism for centuries, long before LLMs were a thing.
See trap streets for one of the better known examples.
I learned about that from Doctor Who!