A derivative work is a creative expression based on another work that receives its own copyright protection. It's very unlikely that AI weights would be considered a creative expression, and would thus not be considered a derivative work. At this point, you probably can't copyright your AI weights.

An AI might create work that could be considered derivative if it were the creative output of a human, but it's not a human, and thus the outputs are unlikely to be considered derivative works, though they may be infringing.

If the original is a creative expression, then recording it using some different tech is still a creative expression. I don't see the qualitative difference between a bunch of numbers that constitutes weights in a neural net, and a bunch of numbers that constitute bytes in a compressed image file, if both can be used to recreate the original with minor deviations (like compression artifacts in the latter case).