Re: but in the account of the person who took the photos
The way I interpret the reporting elsewhere, at least some of the photos were "professionally taken" so that is a possible leak point. Even at that, I expect the celebs have copies of them in their "private" portfolios. So where the loss of custody happened is not clear.
Also, while weak passwords are usually the culprit, remember that isn't necessarily the weakest link. Hackers might also have trawled the password reset questions, and given the obsessions with celebrities, may have cracked those instead after searching the internet for the answers.