There's the rub, isn't it? At a certain point of AI progression, if you don't point it out, no one would know it's AI, as it's indistinguishable from a human creation. Even tools based on AI to detect AI creations will themselves succumb to the fact that the generator AI can use the information gleaned by the discriminator AI to improve; this is in fact how generative adversarial networks work.

I wonder if soon in the future highly skilled humans will have to prove their works weren't made by AI.