Ask DALL-E 2 for Mona Lisa and it will produce something clearly derived from the original work. The ability to recreate items from the training set depends on how these systems are trained, but they are clearly capable of retraining enough to be problematic.

The Harry Potter the movies aren’t the original books, derivative works don’t imply something is the same just that it’s directly derived from something else.

> If I splatter paint on a canvas, does jackson pollock have a copyright claim?

If you’re trying to copy him then actually yes he would. Being inspired by a technique is fine, but the difference is less subtle than you might think.

Copyright cares how something was created, if you end up with ‘random’ patterns that happen to look suspiciously similar to another work it’s extremely unlikely that you came to that point randomly. What’s the odds you would pick the same 12 colors as someone else and apply them in the same order? 12 factorial isn’t a small number and that’s before considering the color selection.