A friend and I built a web crawler that published images to a pool of workers that generated feature embeddings for all faces it found. After indexing all the feature vectors, we had effectively built a search engine for faces powered by images found on the public web.
The results were terrifying and they really affected me in a very negative way. Needless to say, we moved on to other projects. The world is not ready for the harm such technologies can cause.
Our index contained 100+ million faces and the compute costs were obscene.