One of my favorite Facebook features is auto-tagging. It happened to me last night by accident and ended up being one of those very rare moments of using a product where I got a big grin on my face. The feature comes into play when the service recognizes that a photo or video upload happened around the same general time of an event you said you were planning to attend through Facebook's party planning tools. If your photo or video upload occurs within these conditions you'll be prompted to have it automatically tagged and dropped into the event's photos and videos section.
The key to using this feature is that you don't have to plan ahead. Auto-tagging was designed to help seed the photo and video sections of events with digital media without users having to remember to add it later. This simple one-click-to-add feature has likely increased the amount of photos that get added to events in the days that follow.
So how long is that window between where an event ends and when the photos are uploaded? From what I can tell, it's not long. About 18 hours post-party I uploaded two separate images, both of which were taken on the same device and at the event. One was uploaded from my phone while the other from my computer. Oddly enough, neither was picked out for auto-tagging even two hours after being uploaded. In comparison, the one I took (and uploaded) during the hours of the party got flagged for tags almost instantly.
All of this might seem like a lot of fuss over a minor feature, but it could be the precursor for some very advanced tagging automation that's on the horizon. For instance, the pictures I snapped came with geo-locational information as part of the EXIF data. I can see this information when I upload the same shots to Flickr, but Facebook doesn't seem to do anything with it. Take into account that most parties include an address, and the same auto-tagging system could work to retroactively help tag your photos based on time and location alone.
Of course, more important than simply matching up photos to albums (something humans can easily do on their own) is using facial recognition to tag faces automatically. Facebook was one of the innovators in supplying a way for people to tag their friends in photos, which has even managed to carry over well on the iPhone application, but it's time-consuming and doesn't work well with people you don't remember the next day. Having a system that would automatically go through uploaded photos and offer up suggestions of who it thinks the people are based on one part actual analysis and another off the known guest list (provided by the Facebook RSVPs) Facebook could have a very powerful offering indeed.