Facebook has announced that new optional tools are available to help people manage their identity online. Using the company's facial recognition technology, Facebook will have a good idea of when someone uploads your photo (even if they don't tag you).
The new features are said to help users find photos that they are not tagged in. It will also help you know when someone is attempting to use a photo of you as their profile image - this will come in handy in cases where someone is trying to impersonate another individual.
There are, however, some limitation to the alerts. From Facebook:
"If you’re in a photo and are part of the audience for that post, we’ll notify you, even if you haven’t been tagged. You’re in control of your image on Facebook and can make choices such as whether to tag yourself, leave yourself untagged, or reach out to the person who posted the photo if you have concerns about it. We always respect the privacy setting people select when posting a photo on Facebook (whether that’s friends, public or a custom audience), so you won’t receive a notification if you’re not in the audience."
In short, it's always best to review your security settings periodically to make sure you're comfortable with what's available to others!