1. There is no downloaded photo with which the face is checked. 2. So far, do not explain the task for humanity - the result will not. (Naturally, no one will break the faceid mechanism)
You need a library in the language that we decided to write an application. There are many such networks. This is the usual disposal of persons. Faceid, naturally, not related.
I'll say right away - if the phone is very cheap, then the front camera is completely wetting. Hence the minimum probability of the schedule + very low speed of work.
For what to write gathered? and cocoa basic knowledge in the subject?