@Taco_lad @Lana And the part I don't understand is why a ruling what necessary for that. That was already the pre-existing rule.
If the input of a data transformation (such as compiling a program) was copyrighted, then so is the output, provided the output contains a sufficient amount of the input - and vice versa.
The court has just figured out that it makes sense to keep applying this rule even if the transformation process is an AI.
Note that the AI can most definitely also encumber a work with additional copyright. E.g. it is quite possible for Google to train Gemini's image generator Nano Banana 2 such that Google can claim copyright on any image it generates (in addition to any copyright on the prompt and on training data by other people that went into it) - we just don't know whether or not Google did. The obvious way to do so would be to train it exclusively with works Google holds the copyright to. Or to have a system prompt such detailed that any reasonable person can recognize the style (well, we do know they didn't do that).
As such, my recommendation regarding use of AI generated works is to not raise the copyright question. Do not release any AI generated source under an open source license. Do not ask money for any AI generated works. If you absolutely must use AI generated works commercially, figure out with the provider of the AI model how the copyright situation works - if you e.g. can make a contract so they license the generated works to you, then you can claim good faith and they would be on the hook if copyrighted works were replicated.
As an example, Google specifically does not provide a license of this kind. Instead, Google says at
https://policies.google.com/terms/generative-ai/use-policy: "Do not engage in dangerous or illegal activities, or otherwise violate applicable law or regulations. This includes generating or distributing content that: [...] Violates the rights of others, including privacy and intellectual property rights -- for example, using personal data or biometrics without legally-required consent." - so they shift the blame to the user if anyone's copyright was violated, and make the user responsible for any copyright violations in the generated works, even if the prompt never asked to use someone else's work.