AFAIK only people can own copyright (the monkey selfie case tested this), and machine-generated outputs don't count as creative work (you can't write an algorithm that generates every permutation of notes and claim you own every song[1]), so DALL-E-generated images are most likely copyright-free. I presume OpenAI only relies on terms of service to dictate what users are allowed to do, but they can't own the images, and neither can their users.
[1]: https://felixreda.eu/2021/07/github-copilot-is-not-infringin...