I have also done similar project for fun. Link here: https://github.com/sawin0/FaceDetection
For those who don't want to dive into repo.
I have quick suggestion for you, if you have path of circle and face as CGPath then you can compare circle's and face's bounding box using contains(_:using:transform:)
.
Here is a code snippet
let circleBox = circleCGPath.boundingBox
let faceBox = faceRectanglePath.boundingBox
if(circleBox.contains(faceBox)){
print("face is inside the circle")
}else{
print("face is outside the circle")
}
I hope this helps you and others too.
P.S. If there is any better way to do this then please feel free to share.