Privacy and GeoTagging Photos with GPS-enabled iPhone

flickr geotag example map

Being able to record where a photo is taken one of the key features of the new iPhone. Not only does the phone capture a great picture but there is no residual “Now where was I”. You can instantly see where the photo was taken on a detailed map. This is great for geocoding when surveying, but what are the social implications?

Do you want to share this level of detailed personal information?

Why wouldn’t you? Consider this:

Upload a week’s worth of photos.

  • One taken on the way into work of that cute gal you always see at your metro station
  • Another in your office for a coworker’s going away party
  • Another taken at your favorite dance club
  • Another taken at the great brunch place you go to on Saturdays and
  • Another of the pile of laundry you’ve been ignoring all week

Normally you are adding captions and keywords that someone who already knows you can piece together and perhaps guess or already knows where all these physical places are. But you’ve gate-keeped based on “you need to know me and know enough about me” to get it.

Up until now, you’ve controlled the information flow based on how much you tag the photo in the context of how well your online “friends” know you.

Related links: adding GPS locations to photos when you don’t have a GPS (one) (two) (three) (four) (five).

GPS tagged photos are game changing

Now someone who doesn’t know anything about you, and with whom you might NOT want to share that level of personal information, can instantly become your first stalker. They know exactly where you live, exactly where you work, exactly how you get to work, and exactly where you relax and have let down your guard.

Something to consider as an adult and perhaps lock-down if your child has a GPS-enabled cell phone.

Of course, if you’re on a tourist trip and taking pictures of Yellowstone and the Statue of Liberty and are never going to be there again it’s perfectly fine to include the full GPS coordinates since that doesn’t disclose personal information and you’ll not routinely passing by there again. However, if you visit Aunt Mildred in Brooklyn on the same trip you might want to limit access to her home’s location.

I’m invincible, right? What do I care?

Consider the following two situations:

  • I was at a friend’s house party on Friday and took a few pictures and was about to post them when it hit me: I’m potentially compromising her safety, not just my own. If I post those GPS enabled photos some random person could view the photo (hey, it’s up on Flickr for anyone to browse) and know which front door to be waiting at. Skechadellic, dude!
  • I have a swimming hole I’d like to keep on the down-low but when I go out there I take a few shots with my camera to remember the scene. If I post those on Flickr with the GPS coordinates suddenly anyone that views my the photo tagged “My secret swimming hole” can see it placed exactly on that blue map polygon and route directly to it. Not so secret after all. Oops!

So it turns out Flickr has a way to moderate this to an extent. There is a setting to control this, sort of. Screenshot below:

flickr geotags

Notice how I do NOT have this option checked. But my GPS information is still being read in and placed on my account map somehow. Bad!

User Solution 1

The best, fail-proof option is to not record the GPS information when the photo was taken. But then you loose that information for your personal record. The iPhone asks the first time a GPS enabled application is launched if you want to allow it access to the GPS. Press “Don’t Allow” and you’re set.

But once you have enabled the camera to know the location you can’t disable it until the phone is turned completely off and restarted, less than convenient and oh so easy to forget about. You can go to the General Settings area of the phone and turn Location Service on and off without restarting the phone, however.

iphone use current location

User Solution 2

There should be a middle way when uploading and displaying on photo sharing sites like Flickr. This way you retrain full GPS location for your private records but only let out an approximate public location for everyone else.

For the Mac you can download PhotoInfoEditor to edit the precision of the GPS coordinates stored in the EXIF information for the photo (or a duplicate targeted for public upload). I had a devil of a time finding this app as most simply report the GPS coordinates; they do not allow them to be edited. If someone knows of a comparable app on the PC please email me.

Notice in the screenshot below that I have stripped the latitude and longitude to display to the hundredth (39.35° N). You could just as well scramble the coordinates down to the 4th or 5th decimal position when in the city and still be in the right neighborhood but no longer be at the right building. Photosets can be batched adjusted.

This puts the photo in the rough vicinity of the actual location but does not reveal the actual location

. photo info editor screenshot

When you do this before uploading to Flickr or Picasa you can have the benefit of placing your photos on a map with some accuracy but just not with a high precision. In other words, don’t zoom too far into the map or the photo locations become inaccurate. But zoomed out they are perfectly acceptable.

How can software be improved?

On upload / display of the photos in a social photo site:

  • Group permissions for viewing Placename tags and GPS coordinates on map with default being NOT to show the geographic location but to apply limits of precision with individual photo exceptions as detailed next:
  • On / off toggle for Placename tags per photo
  • On / off toggle for GPS coordinates per photo
  • Placename precision (country, state, county, town, neighborhood) from Yahoo or Google geocoder as a slider control per photo
  • GPS precision (exact, 1/4 mile, 1/2 mile, 1 mile, 2 mile, 5 miles, 10 miles, 20 miles, 60 miles) for latitude and longitude as a slider per photo

The GPS precision needs to take into consideration that the number of earth miles at each degree of latitude changes. Simply chopping of decimal places is a crude solution. A more elegant solution would be to add a random ± X decimal degrees to the actual location at the target precision. Even though the iPhone GPS can get you down to 10 meter accuracy, sometimes you don’t want to be that precise.

I’ve already spoken to the developer at AirMe which is my favorite app on the iPhone for uploading to Flickr and he seems interested in making the required upgrades to his application. Please help spread the word to other developers!

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19 Responses to “Privacy and GeoTagging Photos with GPS-enabled iPhone”

  1. Dee Lee says:

    adding a random number is not such a good idea as the original coordinates can be retrieved given enough samples. This applies whether each picture’s coordinates are perturbed by a different random amount or all are perturbed by the same random amount. The original information signal still exists and given enough data points, could be recreated. Think of it as adding static to a sound sample. Given enough repeated notes, the orinal score for certain sections can be recreated. The best way is for all pictures with a certain coordinate range to resolve to a single fixed point. Truncation is one method of doing this. This is like mapping all notes within an octave to a single note. It then becomes practically impossible to retreive the original data.

  2. ces says:

    Also, if you’re like a lot of us and post images to a blog–all while on the go–you’re also giving out TIME information.

    Say you’re spending a weekend out a friend’s beach house and sending photos to the blog (assuming cell reception) for all the other friends who didn’t make it to the par-tah….well, hey, now everybody knows you’re NOT HOME at the moment…

    Lock your doors and photos.

  3. nathaniel says:

    Responding to Dee Lee — What about truncating and then adding a random seed? This way all photos wouldn’t stack up on the same locations. Is this the best approach?

    Without truncation, how many photos at the same effective actual location with individually randomized GPS coordinates is too many (would reveal the actual location)?

    Perhaps the user can be warned when uploading more then X number of photos and have truncation kick in instead of just randomization?

    Without truncation, is the best bet is to apply a single random seed to an entire batch of photos taken an event/set of photos (time X, location Y)? (Which would be grouped according to a granular truncation of time and location.) This would need to take into consideration the accuracy of the GPS when the photo was captured (which varies between 10m and 200m in my experience on the iPhone).

    Say if I take 5 photos in near enough proximity to each other that they are in the same truncation location (but do NOT share the same actual location). Then since they were not in the same actual location I want to add a different amount of noise to each so they are quasi randomized and not stacked up on each other. At this point they would just coalesce around the truncated location which would not reveal the actual location. Seems okay.

    But if I hadn’t truncated them, then after Z number of photos in near actual proximity to each other would the actual location be given away? Seems like after only a handful of photos (3 to 5). This must depend on how course the random number sample is? So if the random number were larger than the truncation’s precision? But that would not solve the problem, just slightly increase the number of samples before the actual location were revealed?

  4. nathaniel says:

    Responding to ces —

    Add on / off toggle for Time/date stamp per photo

    Time/date precision (exact, second, minute, hour, day, month, year) as a slider control per photo

  5. James says:

    My comment didn’t appear so once again, to reset GPS settings of camera without resetting iPhone:
    Reset Location Warnings

  6. nathaniel says:

    Thanks for the tip, James!

  7. Tom King says:

    You use the word “exact” seven times, which makes your blog very misleading. Sheesh, have you actually mapped the GPS coordinates stored in your iPhone photos? “Exact” is hardly accurate.

    If your message weren’t so shrill, you might mention that GPS tags probably aren’t accurate enough to find Aunt Mildred in Brooklyn. They would narrow it down to a few hundred homes, but wouldn’t really take you to her front door, as you suggest.

    You also fail to mention that sometimes the iPhone uses cell towers to *approximate* location in the absence of a GPS sat signal. Photos at your friend’s party, away from GPS satellites, would contain location tags probably be off by blocks.

    Just to check myself, I grabbed the first Flickr photo taken in my home here in Los Alamos, New Mexico. Good luck finding me, it’s off by *nine* blocks.

  8. Fred says:

    Tom King, your iPhone (and my iPhone) use the cell towers to generate the location, but the iPhone 3G and my iPhone 3GS have an actual GPS chip, and the accuracy is under 100 feet. On my iPhone my current location is a 800′ circle. On my iPhone 3GS my current location is a dot 15 feet from the chair I’m sitting in as I type this, so Kelso’s comments are entirely accurate (pun intended).

  9. Gary Holster says:

    Ya..its amazing what people geo-tag. Browsing through flickr images using respotter and lots of parents put up geotagged photos of their kids pics for public view…

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  15. Joy says:

    For iPhone to turn off location option click on setting then general then restriction enter your password if you have enabled it and then click on off for location option

  16. Photoguy says:

    I recently found an iPhone application lets me remove geotags from photos before they are shared and it’s Free. I figured it was worth a try, and it’s actually pretty good.

    Here’s the link if anyone wants to check it out:

  17. [...] Privacy and GeoTagging Photos with GPS-enabled iPhone [...]

  18. justin says:

    Great article. 5 stars! Keep up the great work!

    Please stop taking pictures of my girlfriend at the metro station. Stop using your camera at the dance club. Do your laundry. You stink. Nobody cares where you and your friends party. Nobody gives a sh*t about where your Aunt Mildred lives. And seriously dude…. your “super top secret” swimming hole? We’ve been swimming there for years.

    There is a a little switch under SETTINGS>LOCATION SETTINGS> and then whatever app you don’t want stalking you.

    And after your pulitzer prize winning, fear mongering, big brother is watching me article…. i still can’t figure out how to use the GPS coordinates iPhone provides so I may stalk myself in Google Earth. At least I can still use my flikr account to look it up?

  19. TechTeria says:

    there is no doubt on the abilities of iPhone as they have made it a no one smartphone in the world. Really amazing! :D