It's just procedural generation, I don't think that just because someone could follow the same steps as you to produce the same thing that it can't be your intellectual property, otherwise how do people claim ownership of anything made in software? You could call the mouse and keyboard inputs "prompts" if you wanted, Dall-E is just easier to use.

In fact you could make a very simple neutral network that turns a seed into an image, that is capable of generating any image. The seed would just need to be as big as the output. That wouldn't invalidate my ability to have intellectual property on images just because someone could produce the same thing with the AI with the same input.

In fact we should expect that as image generators get better, eventually we should be able to generate pretty much anything with them with a detailed enough prompt, I don't see why this would affect the ability to own the outputs.

They made a blog post about this. They generated a lot of samples and checked for matches in the dataset, there were some, mostly very simple vector art that was duplicated many times over in the dataset.

They removed the duplications and then checked again, no matches.

https://openai.com/blog/dall-e-2-pre-training-mitigations/