A car mechanic finds a stash of child porn pics in the trunk of a car as he replaces a burnt out tail light. By your standard he shouldn’t report it?
This is like the guy at Moto Photo going thru your pictures when you drop the film off. If someone there saw a porn photo of my child and did not say anything, I would get him on harboring a criminal, or an accessory of the crime, or knowing after the fact. Either way, I can’t imagine anyone siding with this guy.