Generative AI and Copyright

I recently came across an interesting article (https://news.bloomberglaw.com/ip-law/wild-west-of-generative-ai-raises-novel-copyright-questions) about an artist who registered US copyright for a comic book made with the assistance of artificial intelligence. The US Copyright Office later revoked its decision of granting the copyright because it had “overlooked the use of AI in the creation of the comic.”

However, people use the help of AI to create work all the time, it’s just that the degree of the AI’s assistance differs. For example, a drawing software that allows a user to draw a smooth line when the actual motion of their hand is not smooth uses AI to touch up the lines drawn by the user to make them more presentable. Works generated using this amount of assistance from AI is copyrighted all the time. But, as we can see from the article above, works with images created by AI based on an artist’s prompts and vision cannot be copyrighted because too much AI was used. So, what is the maximum amount of AI contribution that is allowed for an artist’s work to be able to be copyrighted? At what point does it cross the threshold? Where should the threshold be? At what point is the work no longer solely the artist’s work, and at what point is the work no longer “original” in terms of copyright law?