Now, Google is rolling out its face-grouping feature across Europe. The feature was available in some regions since 2015, and it works by looking at all the photos on your device and creating a model of each face so it can group similar instances together. Then you can search your photos for particular people or create albums or movies of them.
If that sounds like an overstep of privacy, Google tries to mitigate this by making face groups and labels visible only to you. The face groups aren't shared when you share your photos, so theoretically they are only a tool for organization of your own photos. If you'd rather not share that much information about your friends and family, however, you can disable the feature to delete the face models saved on your device.
If you do enable the feature, you can find the face-grouped photos under the "People Explore" view. It even works with pets, according to Google.
If the automatic face detection doesn't work as well as you want, soon you'll also be able to manually tag faces, according to Google Photos' product lead David Lieb.