According to Google Vision API documentation. It doesn't support Face Recognition, only Face Detection and other attributes detection such as lable, landmark, web, label.
Face Detection : detect multiple faces within an image, along with the associated key facial attributes like emotional state or wearing headwear. Facial Recognition is not supported.
Label Detection : Detect broad sets of categories within an image, ranging from modes of transportation to animals.
Explicit Content Detection : Detect explicit content like adult content or violent content within an image.
Logo Detection : Detect popular product logos within an image.
Landmark Detection : Detect popular natural and man-made structures within an image.
Image Attributes : Detect general attributes of the image, such as dominant colors and appropriate crop hints.
Web Detection : Search the Internet for similar images.
Optical Character Recognition : Detect and extract text within an image, with support for a broad range of languages, along with support for automatic language identification.
Check out more details : https://cloud.google.com/vision/
Hope it can help you and more ideas and concepts
Google Face Recognition API
, it probably doesn't exist. – Fallal