I'l try to go thru all the techniques I know and I've used to add geographical information to pictures, so they can be mapped to an actual point on a world map.
Why flickr ?
Because it's the online service I use to expose my photos to the world. Some of the techniques explained here can be used with other services - but as I don't use them you'll need dear reader to find the tweaks needed.
Using the provided map
Is probably the best solution. You just snap the picture and when you upload it you move it to the proper spot on the map.
- Easy to use
- Some maps are incomplete so you can't geotag that way
- Where do you put the picture , where you where or where the subject was
Using an external GPS source
This requires a little bit more of hardware than your camera - but you will be able to geotag pictures where the map isn't accurate enough (like for say this picture). You'll need your camera, a gps device capable of logging gps coordinates and some software. The software will match pictures and longitudes and latitudes. The way this work is quite simple : each time the gps write a log entry it also logs the time. When you press the shutter button, the camera also records the time. The Piece of software will read both files and do a matching based on those time stamps (I use GPS photo linker on my mac, and heard good reviews from geosetter).
- Not too complex
- Tags anywhere on earth
- More post processing
- cost of the device
- need to think about some extra batteries for the device
Using alternate services
I know of at least two. They both use google maps which is the most accurate maps available for free online (AFAIK). And they will geotag your pictures using the flickr API. These services are http://loc.alize.us/ and http://maps.yuan.cc/. They both use the same data , and I have noticed any differences using those services. I did use use these services because I didn't always have a GPS, or the gps with me.
Last but not least I've just found out a nice way to geotag pictures taken while flying on planes the explanations are here.