10/28/2019
Just had a case where this happened. There was a question as to how certain "nasty photos" appeared on an iPhone that was in the possession of a child who was the object of a child custody battle. The parents were accusing each other of corrupting the minor by allowing him to have such pictures when, in fact, they were cyber flashed to him. The iPhone database that manages the photos on the phone has a field that stores the creator package or process that creates a photo on the phone. It is of course a deep forensic dive, but the proof was there. Air Drop was the culprit and the settings were for everyone. Air Drop's package name is com.apple.sharingd. There were a handful of images and the thumbnails were created at the same time, to the second.
People use Apple's AirDrop photos to send unwanted explicit photos to strangers. Here's how to change your settings to prevent people from being able to send you images without your consent.