What if I use water colors and create a alien planet? Did I do so from my own imagination, or was I inspired by a book, and if so, did I create the painting for a book cover?
All of the above is nice and clear cut, or about as much as can be expected.
Not really. There have been lots of recent lawsuits where a songwriter or band you've never heard of sued a famous band or musician because some part of one of their hit songs sounds like an earlier work. Two that come to mind are Men at Work's
Land Down Under and Ed Sheeran's
Shape of You. These sorts of copyright infringement lawsuits are becoming their own industry. I wouldn't be surprised if they're even using deep learning models to scan massive music archives for similarities.
So, I'd expect that, if a painting or CG work would sell for $millions, then someone would probably come out of the woodwork and claim it was a ripoff of something they posted up on DeviantArt. Maybe it's even happened with movie posters?
can AI do so without copying and pasting it together?
Yes. Generative AI doesn't store actual images, in whole or in part. Not if it's trained properly, at least. It learns rules and patterns, and those are what it uses to generate new content.
Training is a key part of the question, though. If you only trained it on pictures of the Starship Enterprise, and then asked it to produce an image of a space ship, you could almost bet it's going to draw something with striking resemblance to the Starship Enterprise. If you trained it on a wide diversity of sci fi art, then the space ships it generated would still be largely derivative, but no less so than what many human artists would tend to produce. You'll also probably see some interesting "original" ideas, which are variations, combinations, or extrapolations of rules and patterns it learned that a human might not think to produce.
Whatever the case, if an AI-generated image looks similar enough to one drawn by a human (and probability suggests it'll happen, even if the human's wasn't in its training set), litigation will likely follow.
On the flip side, we know people are using AI-generated content for inspiration & more, and I'm sure it often goes uncredited. Not to side with the AI, but just to point out that the situation is very asymmetrical.