https://mahmoud-salem.net/the-invisible-shield
This is where the engineering meets the ethics.
Every false positive means an innocent person's content was flagged — a family photo, a medical image, a piece of art. It means unnecessary investigation, potential harm to reputation, and erosion of trust in the system. At scale, even a 0.01% false positive rate means thousands of wrongful flags per day.
Every false negative means a child's abuse was missed. An image that should have been caught slipped through. That child continues to be victimized every time the image is viewed, shared, or traded. The distribution never ends.
There is no threshold that eliminates both. Setting the threshold is a moral decision, not just a technical one.
In practice, the industry errs heavily toward minimizing false negatives — catching every possible match — and then uses human review to resolve false positives. This means the system flags aggressively but confirms carefully. The cost of a false positive is an investigation. The cost of a false negative is a child.