Presumably there is some level of traceability to this. If a falsified photo is found on a document used to commit fraud or other crimes, the photographer who enabled it would be banned, blacklisted, and possibly held criminally liable.
What prevents me from stamping "Walmart at 123 Example Avenue" then scrawling an incomprehensible signature on any photo I want? The stamps the shops use don't have any security features to them.
Unlike the old "guarantor" system where a licensed professional or public official (judge, lawyer, doctor, etc.) had to sign your application - basically, people who the government could verify the existence of and hold accountable - there's not very much traceability to the photo system.
Canada's guarantor system is still in place, although the guarantor currently doesn't have to be a licensed professional.
As an American immigrant to Canada, I don't see the point - the US has never in my lifetime had either a professional photo requirement or a guarantor requirement for its passports, nor even a digital requirement.
Certainly, paying someone like a pharmacy for passport photos is not rare in the US to reduce the risk of out-of-spec photos leading to a rejection. But that's just a common personal choice and not obligatory.
I suspect Canada's guarantor system is inspired by the UK's, though I don't actually know.
