[freedompeace]

How could Facebook do this (technologically)?

According to a redditor,

"

- It's not IP address. Facebook successfully identified a number of specific locations (bars, theaters, etc) even though I had uploaded the photos from my home

- It's not geo-tagging. All of my photos were taken with a camera that does not geo-tag (Nikon d700).

- It's not contextual tagging. There were no people tagged in the photos, no comments in a lot of them, no words or phrases or names in the captions that could have given clues

- It's not image recognition. One set of photos was taken at Cafe du Nord in SF, CA and every single shot was of the performer onstage, with no identifying characteristics or clues to be had.

"

I would really like to know as this is very interesting and none of the reddit comments (as of now, 12 hours after submission) really answer this question. What technology or methods are they using to suggest (accurate?) locations where pictures have been taken from?

Even more strangely, I have never used my mobile phone with Facebook, but when I uploaded a photo just now of a place from my childhood to which I haven't ever been since using Facebook, Facebook correctly suggested the location.

What the heck?!

[loopdoend]

Purely speculation but perhaps he is carrying his phone with him and it is correlating his location with the timestamps on the images, or perhaps he marked himself as attending an event which is at the venue.

From an image recognition standpoint, if anyone else was at the event and took similar sets of photos which they then tagged, that could also be used.

[iradik]

This is how it can be done without any EXIF/GPS data with a fairly dumb algorithm.

It's a picture of a baby at a hospital.

There are probably hundreds of baby photos being taken per day at that hospital being posted to FB. Some have GPS and some don't.

The images that do have GPS, get recognized and lumped together as the same "entity" since they all look the same.

FB then looks up where she lives, then looks for any photos that don't have a location (like her baby photo), then tries to match it with any photos within a 50 mi proximity to her hometown. Bingo finds 90% match on the baby pic in the hospital, and asks user for verification. She says YES, then this pic gets lumped together with all the other entities. FB also asks more often since it's "right".

[hyperbovine]

A slightly more sophisticated approach would be to use the all /other/ data they have on her to predict what hospital she is likely to choose. Why stop with just her hometown?

[iradik]

Sure let's speculate they have a function that returns a guessed gps coordinate at time t. Again there are dumb implementations for this. Can take a time decaying and time-of-day/day-of-week weighted mode of your recognized locations. I imagine it'd be fairly accurate.

[missing_cipher]

Could be as simple as figuring out that the picture is a baby, get the user's location and then find near-by hospitals. Then ask if the guess is right.

[ddw]

But you can take a baby anywhere. Unless FB deduced "this baby was born today" and figured it must be at a hospital.

If so, we're in trouble...