Any of Facebook's over 400 million users will immediately recognize some new features on popular Twitter photo-sharing service Twitpic today as users can now tag people in their photos. In a blog post this morning, the two-year-old company announced it had passed the 10 million user mark and that it sees 40 million unique visitors each month. The company says it is releasing its Face Tagging functionality "to show [its] thanks" to the community, but could it bring headaches and worries with it too?

How It Works

Face Tagging literally works exactly like tagging photos on Facebook. While viewing a picture, the text "In this photo:" is displayed below it with a link to begin tagging the photo. By clicking the link, users can then pinpoint people's faces in the photo and a box will appear around the face, as well as a pop-up dialogue box in which to enter the person's name and Twitter handle. Once done, users hit the "Done Tagging" button to return to normal browsing functionality - just like Facebook.

Honestly, the only difference between tagging photos on Facebook and on Twitpic is that the "Done Tagging" button appears above photos on the former and below photos on the latter. While Twitpic's new functionality is a dead lift of Facebook's long-existing photo tagging feature, it is smart to copy the social networking giant. Why re-invent the wheel? Instead, Twitpic is giving users a familiar experience, making the process easy and intuitive.

How It Doesn't Work

When users tag a face in a photo, by default they can send a rather dry tweet announcing the tag and including the user name of the person tagged, effectively working as a notification. First of all, the inability to personalize this message is a bit of a downer, but you can always just uncheck the box and send out the tweet yourself.

Additionally, the only way Twitpic alerts users that they have been tagged in a photo is via Twitter - so users could be tagged in hundreds of photos and not know it if the tagger chose not to tweet the tags. Users do have the ability to delete tags of themselves on other people's photos, but right now the only way of knowing of such photos is to be sent the tweet, which not everyone will choose to do.

In a phone interview today, Twitpic founder Noah Everett told ReadWriteWeb that additional features, like the ability to view photos you're tagged in, are in the works and should be out in a few weeks. The goal, he says, has been to launch the tagging feature and use user feedback to determine the next logical step.

What About Privacy?

That next logical step, for many users, may be privacy controls - something the new feature lacks. On Facebook, users have the ability to manage photos they have been tagged in and remove their association from a photo once-and-for-all. The only option related to photo tags for Twitpic users is the option to allow other people to tag their photos. Everett says Twitpic is looking into possible privacy controls, such as a blanket rule preventing anyone from tagging you, or specific user-based bans to avoid those "crazy ex-girlfriends", as he put it.

Personally, I use Twitpic mainly as a means to an end - I upload photos to the service for sharing on Twitter via a mobile application, which means I don't visit the Twitpic web interface too frequently. How am I supposed to know when I'm tagged in a photo if the user tagging me chooses not to tweet it? Even if I visit the Twitpic homepage, there is no way for me to view an aggregated list of photos I am tagged in and no system for notifying me of such photos.

Everett says the company is considering ways to notify users, including email alterts, but hopes that eventually app developers will add the functionality using Twitpic's API. I guess the good thing is if someone decides to surreptitiously tag me in a photo, for now the general public has no real great way of finding it either.

An Impending Headache for Data Fans?

The other important thing to note from the launch of Twitpic's Face Tagging functionality is that it is a new stand-alone platform on a third-party Twitter application. What that means is that compatibility between networks is completely up to Twitpic. When other Twitter-based photo sharing apps add this functionality (which they are likely to do), it will be nearly impossible for users to effectively aggregate their tagged photos (and other meta-data) across platforms.

I spoke with Thomas Vander Wal, father of the phrase "folksonomy" which refers to collective tagging of meta-data, and he shared some interesting insights into this situation.

"Since others have done similar things on other platforms (Facebook, Flickr) the [intellectual property] is fuzzy and Twitpic can't claim it, so others are free to jump in," Vander Wal told ReadWriteWeb. "It would be in Twitter's best interest to build a central aggregation point for this."

This is exactly why Twitter is rolling out annotations, which have been testing recently and should be out soon. The annotations will create a standardized framework for third-party apps to build from, making interoperability between services much easier. Everett said he actually spoke with people from Twitter today about "coming together" and "rolling [tagging functionality] into annotations."

Strangely, however, Twitter mentioned in April that it planned on having "trending annotations" and letting developers battle for standardization. It would make sense that meta-data for tagged photos could be added to Twitter's annotations, and if the services adopted the standard, aggregation would be simple.

If not, then the entrepreneurial community, "somebody like PixelPipe" as Vander Wal suggested, would need to create another third-party Twitter service that would handle this aggregation - not an ideal solution going forward. We can't blame Twitpic for this fate: what the company is doing is good in terms of pushing the platform forward. We can, however, bring up the privacy issues Twitpic has raised with their new service and its apparent lack of controls, but then again, it is a brand new feature and more functionality is on the way soon.