Adding model provenance would be a good idea so you can support multiple. I was wondering if DALLE 2 embeds any metadata in the images but haven't had a chance to investigate.
I also think you should consider adding the option to clarify copyright status ... in particular, allow users to dedicate the image to the public domain via CC0 (https://creativecommons.org/share-your-work/public-domain/cc...), or maybe put it under a CC BY license. May be debatable what the legal status of the images is, but a CC0 dedication would at least get rid of any ambiguity.