Because of the inevitable photolocationfinder dot com that will immediately come into existence if they ever succeed.
Then everyone who hates someone or likes someone way too much, will only need a couple of photos from twitter or wherever, to know where to look for that person in real life.
It's not likely that a computer vision system is going to be that much better than humans at the task. Maybe it will be able to guess your latitude by the color of the sky or something crazy like that, but not give you an exact address.
It is not unreasonable to believe that an algorithm could key in on architectural peculiarities of a given region. On top of that, if there are any people who are in the photo who share their address on facebook, twitter, foursquare et. al. it is game over.
Roughly map the topology of the ground in the background of a photo, then use clever algorithms to match that topology with real world maps of terrain.
Automatically match iconic buildings to those in a database.
Have a list of features that are different from nation to nation, or region to region, and match them. Electrical outlets, road signs, road markings, fire hydrant colors, and match them automatically.
Have a list of different geology. Light coloured rock in this region, reddish soil in that region, very flat terrain, very undulating terrain.
This is what comes to mind in one minute of thought. None of these would be effective on their own, but combined you could probably get surprisingly close.
If you don't want photos online, don't take photos with a smartphone. Pretty sure digital cameras don't autoupload (at least the cheap ones I have had). That said, we have a signal and noise situation - if everyone's photos are online it becomes difficult to target any one person without a very good reason.
Does this strike anyone else as being a bad idea?