The issue is not just a matter of failing to provide attribution.. The issue is that you have NO right to use the photo in the first place. That is left of another person's property.

Hive account@steemcleaners was right to ding you for it. I'm rather curious how they managed to find it behind a paywall, but, if they were to tell you then you'd be able to steal more content. That is not a good plan.

For all you know, one of the volunteers has an account and it was your bad luck day.