MacRumors:

Over the weekend, a Reddit user discovered a few lines of code within the framework of Apple’s beta of the macOS Sierra Photos app, possibly detailing both the specific facial expressions that the app recognizes and every single searchable object users can find in both Sierra and iOS 10.

In a more detailed Medium post, Redditor vista980622 explained that Photos will be able to “recognize and distinguish” 7 total facial expressions after the app scans a user’s library and forms a “faceprint” for each individual in a picture. The expressions include greedy, disgust, neutral, scream, smiling, surprise, and suspicious.

If you are interested in the specifics, here’s a link to the Medium post that lists both the facial expressions and the objects Photos can recognize. I can only imagine this is just the beginning.