In the web version of Nic or Not, the project uses face recognition to detect if a person is or is not Nicolas Cage. You can drag in your custom photo, or click on the provided selection at the bottom. This project uses TensorflowJS via the face-api.js library.
In the iOS version of Nic or Not, the project uses React Native on top of CoreML to run the faces through a recognition recognition model. You can simply point the app at a face and see the indicator pop up. This project uses CoreML via the react-native-vision library.