Exactly, if some whistleblower is going leak a picture of some classified documents, the intelligence agency could simply upload a picture of the documents to the database. And bam, the journalist is arrested.

Moreover, if the database doesn't store actual images and instead only the perceptual hashes, it would be impossible to audit, even if the auditor has access to the database.

All the auditor would see is a bunch of hashes, they wouldn't be able to tell which hash actually represents CP and which hashes represent pictures of confidential documents.