This must depend on jurisdiction, but in most western legal systems it's called "Possession of Child Exploitation/Abuse etc Material". Some material that might strictly fit into the age category is not CEM due to some other merit, especially when borderline- ie is art. We have case law for that where I live. 2ndly "possession" is formed by 2 elements- knowledge and control. Can't have it without them. Now you may live somewhere with different law, but this is pretty standard.