MAKE describes ‘HOW TO GPS tag photos’.
Here’s an example of the Flickr tags:
And they recommend including ‘http://www.geobloggers.com/’ in the description, so your photos will automatically be referenced by GeoBloggers.
The problem is that unless you have a very rare GPS-enabled camera, you’ll have to carry an external GPS and keep track of the coordinates of where each photo was taken. So it’s just a system for geeks for now. Still, pretty cool.