Public domain gets assigned automatically when some time has passed or by the author releasing it into the public domain under the cc zero license. Unsplash started like that. There are potential issues like uncertainty about signed model release documents when people are the main part of the picture plus trademarks prominently appearing.

it’s complicated

Just realized I did not really answer the question.

One is a license for all commercial use. Creative Commons is more restrictive: https://en.wikipedia.org/wiki/Creative_Commons_license.

It's not clear what 'commercial use' means.