Using CoreImage to detect faces

coreimage_face_example.swift

import CoreImage

extension UIImage {
    func rectsForFaces() -> [CGRect] {
        guard let cgImage = CGImage else { return [] }
        let ciImage = CoreImage.CIImage(CGImage: cgImage)
        
        let options = [CIDetectorAccuracy: CIDetectorAccuracyHigh]
        let detector = CIDetector(ofType: CIDetectorTypeFace, context: nil, options: options)
        let hallOfFaces = detector.featuresInImage(ciImage)
        
        return hallOfFaces.flatMap { feature in
            guard feature.type == CIFeatureTypeFace else { return nil }
            return feature.bounds
        }
    }
}