Certain new cameras have geotagging features already built in; however, you can do this manually using Google Earth and Geotagger.
Download Google Earth from here to your desktop.
Download Geotagger from here to your desktop.
Double click the Google Earth dmg on your desktop to mount it and then drag the Google Earth icon into your Applications folder.
Double click the Geotagger dmg on your desktop to mount it and then drag the Geotagger icon in your Applications folder.
Double click Google Earth from your Applications folder.
Navigate to the location your image was taken. Make sure to center the location in the window.
Double click to launch Geotagger from your Applications folder.
Now drag a photo onto the Geotagger icon in the dock. The GPS co-ordinates from Google Earth will automatically be written to your photo.
Now you can drag the photo onto the iPhoto icon in the dock to import it into your iPhoto Library.
Select the imported image and press Command+I on your keyboard to view the GPS co-ordinates you added.
It is possible to modify iPhoto to reveal a hidden Show button which will automatically open Google Maps to reveal the location of your photo. This will be covered in an upcoming tutorial!
It is also possible to create Flickr maps using the geotagging on your iPhotos!