Flickr has recently added a number of functions to their API to give developers access to their People in Photos functionality, which allows individuals to be identified in photos uploaded to the service.
A good way to get a sense of what you can do is to look at the 6 new functions added to the API:
Face recognition and tagging has been a feature of other online photo galleries like Picasa Web Albums and iPhoto for some time now, although programmatic access to this functionality is still to be implemented for these services. While Flickr does not have the ability to recognise faces itself, Polar Rose can be used in conjunction with Flickr to detect and tag people in your online albums.
The new API methods respect the opt-in and opt-out options provided by Flickr (with the ability to remove yourself from individual photos), which is one of the advantages Flickr has over Facebook.
To see more examples of how the Flickr API has been used take a look at our list of 498 Flickr mashups.