An article from Jeremy Markel is featured here:

"Geotagging photos is a fun and easy way to enhance your photo experience. Essentially GPS  data is ‘added’ to a photo that will allow it to be displayed on a map. This can greatly increase photo viewing by allowing you to see exactly where a photo was taken.  This assumes that one does not have a gps capable camera which can do this automatically.  Obviously there are a couple of things that you need to make this easy. 
1. Computer. Geotagging can be performed quite easily with both mac and windows, and I would assume Linux although I haven’t tried it.  For software, there are a number of programs that can do this. I use Geosetter (www.geosetter.de/en) as it is an easy to use and effective program that runs on windows and Garmin’s Base Camp software which recently started including tagging capability. Base Camp is
free and runs of both mac and windows.  Base Camp does, however, require maps to be purchased from Garmin if you wish to see the any map aside from the world ‘base map’. Geosetter on the other hand, uses google maps, so as long as you have an internet connection, you can see maps. Geosetter also has the ability to export to Google Earth.
2. GPS capable of creating tracks, which should be pretty well any handheld on the market these days, or another compatible device with software, such as an iPhone. I use a Garmin Oregon 550 and the iPhone app, MotionX GPS, depending on what/where I am tracking.
3. Camera. Nothing special. Any camera will work but you will need to ensure that date/time is correct. Geotagging depends on this. I have a Nikon D70S and a Sony W350 that I use for photo taking.
Basically the procedure is as follows.
1. Transfer photos to computer. The photos will can be organized however you see fit. Organizing into folders that will match tracks does make it a bit easier.
2. Copy GPS tracks to computer. To make this easier to manage, it’s a good idea to name the GPS tracks based on location or other factors. The default name does tend to be just the date/time the track was taken.
3. Combine the photos with the gps tracks.
4. Enjoy looking at where your photos were taken on a map!
Steps using Base Camp
Base camp works the same on both mac and windows.  The first thing to do is to import your gps track. Once this has been done, you will see a track on the map and be able to view each of the points in which the track was created.  Base camp organizes tracks into ‘lists’ so I prefer to create new smart lists that I name based on where the track was recorded. Once you have created a new list, copy the track into the list,
and select the list. You will see the track below the list at this point. You can now right click the track and select ‘Match Photos to Track(s)’. This will open a box that will allow you to add one or more photos to the track and there is a check box that will allow you to permanently geotag photos that you will probably want to check. This writes the gps data to the metadata of the photos.  Note that there is a Time Shift option here as well that you can use to make changes to the data in case the camera’s time does not match the gps track’s time.  After the tagging, the map will show the photos along the track! And other programs that can read this data will also display the photos on a map. These photos are now tagged and if you right click them in windows explorer and view the properties, you will see longitude and latitude info in the file.
Steps using Geosetter
Geosetter is a windows only application that is free and uses google maps for map data. That has an advantage over Base Camp which relies you having purchased Garmin maps. Geosetter is much like a photo browser in that it shows photos/folders as thumbnails. Geosetter also has a lot of additional options that are not covered here for other changes. See the geosetter help pages for info on how to use those options. Within the program, browse to the folder that you wish to tag and select all the images. With the images selected, click the images menu and select ‘Synchronize with GSP data files’. You then choose where the data file(s) are located. I prefer to use the option ‘Synchronize with a directory containing Data Files’ as I leave all my tracks in one folder. You can also make time adjustments if needed. Geosetter will now read all the tracks and determine which ones are applicable to the photos that are selected. At this point, it will then offer the options to tag the photos as well as note how many photos can be synced.  Once photos are tagged you will be able to see them on the map.

At this point, as well, you can choose to export to Google Earth. Exporting to Google Earth will create a KMZ file which can be shared with others and viewed in Earth and you have the option of what size the images will be exported. Photo size can be quite important for sharing over the internet. This file will contain both the track and the photos, which will be placed along the track where they were taken that will be viewable on a map.  KMZ files can be easily shared via email or a web page and can be opened with Google Earth.  I have two files available for download to see how a KMZ file displays. Download the files and
open with Google Earth to view.       www.markelnet.com/files/fussen.kmz"