A comment the mysterious John made on a previous post has got me thinking: what metadata can we get for free in a mobile context, without any intervention from the user? What can I automatically tag a photo (say) with when I take it? So far I've got:
1. Who I am: my phone number and some sort of ID (phone number, IMEI, bluetooth ID, whatever)
2. Where I am: cell ID, country (inferred from the network I'm on, or my phone number perhaps) GPS co-ordinates, postcode (or whatever networks can offer)
3. When I am: what time-zone, what time of day, date (and therefore day/night, season)
4. What format (JPEG, PNG) and size my image is.