In the first you have spent a nice day out with a group of friends. Many of you took interesting photos which have all now been uploaded to Flickr. It would be nice to easily be able to find all of those photos and perhaps automatically create one URL that will show them all.
In the second scenario you’ve been out taking photos of some tourist trap. You’ve uploaded your photos to Flickr, but you’d like to see if anyone else was there taking photos at the same time. Or maybe six months ago before a particular building was knocked down. It would make it easier to find coincidences like this.
In both cases you would need to match photos on two kinds of data, the location of the photo and the time that it was taken. In the first case, you’d also want to filter the matching photos so you only get photos taken by your friends.
Flickr knows which photos are taken by your friends. That’s not a problem. And all digital cameras include the date and time data attached to each photo. And Flickr has access to that information. Of course this relies on the clock in the camera being correct and ignores any timezone issues.
It’s the location information that is interesting. Of course in the future we’ll all be using cameras that contain GPS units so that data will be included in the photo data in the same way as the time currently is. But tha’ts still a few years off and I want this system now. There are already standards evolving for “Geotagging“, but doing that manually for every photo would be incredibly painful. There are people who carry a GPS with them at all times and can get this information by comparing the GPS data with the timestamps on their photos – but I’m not one of them. And I can’t see that procedure getting mainstream acceptance.
So I suppose we’re left with using the existing tags. Most people seem to tag photos with some kind of location information. But in most cases it’s probably not precise enough. And, of course, different people use different formats for their tags.