Nudity, however, is not in itself a sexual act, much less a criminal act. It is a condition of life itself. Artists in all media base their creative work on what they see around them. Writers write about their family's daily life. Painters paint their wives bathing, the groceries on the table, the unmade marriage bed in the morning light.
Photographers photograph their loved ones doing all kinds of things.
And, predictably, a lot of the time those kids are buck-naked. This never used to be a problem. In some states, they even passed laws making the photo-processing companies liable to prosecution if they failed to report any such material. Corporations are prone to cooperate with the authorities in such matters, naturally, especially if there's a penalty involved. So, understandably, they've tended to err on the side of caution, reporting everything, and leaving the decisions up to the police.