A man had a bunch of legal photos of little girls in the same folder as legal adult pornography, and I believe he was arrested with criminal charges filed against him. I read an article about this easily 10+ years ago, so my memory may not be accurate as to the details.
This is from a UK website:
"Many people who have accessed sexual images of children believe that there is a ‘grey area’, between material that is legal and material that is illegal.
We believe that there is no grey area:
Non-sexual images of children: If you are viewing any image of a child for sexual gratification, regardless of whether the child is nude, semi-nude or clothed, then this is not appropriate. The police may investigate the possession of multiple images of clothed children."
As a hypothetical, in an English-speaking country, if someone did this I think they would possible be able to secure a search warrant. Even if they didn't find anything illegal that person's life would be over and it would be more or less "mission accomplished."
Charges were dropped, but were still filed (yes nude but still, nothing should have happened at all):
"In 2014, the Supreme Judicial Court of Massachusetts found that certain photos of nude children, culled from ethnographic and nudist publications, were not lascivious exhibitions and hence were not pornographic; the court ordered dropping of charges against a prisoner who had been found in possession of the photos."