Validating identity. Canadian passport security was crap and there were several high profile cases (e.g. Millennium bomber) of them being used for terrorist activities.

Your photos also need to have the name of the studio stamped and signed in the back.

Government suspects fraud? Call the references (they are generally licensed professions). Suspect the photo? Call the studio or send someone down.

It’s just traceability for the key claims in the application and biometric data.