Returns a character vector of available face detection backends.
Details
Available detectors (in rough order of accuracy/speed tradeoff):
retinaface - Most accurate, recommended for research
mtcnn - Good accuracy, moderate speed
mediapipe - Fast, good for real-time
opencv - Fastest, less accurate
ssd - Fast CNN-based
dlib - Classic HOG-based
yolov8 - YOLO-based detection
centerface - Anchor-free detection
skip - Skip detection (use full image)