Geotag has some aspects that can be configured by you. They can all be found in the window that opens when you select File->Settings from the menu bar. Here is a brief description of each of those settings:

General settings
Mouse click count to edit
By default Geotag starts editing a value in the images table as soon as you click on it. Some users (including myself) find this irritating, as it makes selecting images without editing values complicated. If you change this setting to 2, you will have to double click on a value to edit it.
Font
I like to use a slightly smaller font than the Java default font. Click on the button next to the text field to select a font that suits you.
Show thumbnail images in tooltips
Normally Geotag extracts thumbnail images from each picture while you hover the mouse pointer over its entry in the images table and displays them in tooltips. This can use a lot of CPU time, especially for RAW images. Unselect this option if you don't want to see thumbnail images in tooltips.
Thumbnail size
Here you can change the size of thumbnail images Geotag generates. The size is the size of the longest side of the thumbnail image in pixels. This size is used both for thumbnail images shown as tool tips for images and thumbnails exported to KML files for Google Earth.
Always write to XMP files
Select the check box to always write location data to XMP sidecar files. Click here to find out more.
Check for updates
When Geotag starts up it quickly checks the file http://geotag.sourceforge.net/version.txt, which contains the latest version number. Geotag pops up a message if a newer version is available. This is useful if you don't use Java Webstart to run Geotag. If you do use Java Webstart to run Geotag, updates are automatic and you can uncheck this checkbox.
Distance unit
Here you can choose if distances will be displayed in kilometers or miles.
Altitude unit
This is where you choose if you want altitudes displayed in meters or feet.
Coordinate format
There are several ways Geotag can display latitudes and longitudes. Here you can choose the one you prefer. The options are:
  • ±D.dd° Degrees with decimals
  • ±D°M.mm' Degrees then minutes with decimals
  • ±D°M'S.ss" Degrees then minutes then seconds with decimals
  • H D.dd° Letter followed by degrees with decinals
  • H D°M.mm' Letter followed by degrees then minutes with decimals
  • H D°M'S.ss" Letter followed by degrees then minutes then seconds with decimals

The H represents one of the letters N, S, E, W. I'm used to the letter H from Garmin GPS units, but have no idea what it stands for - any suggestions? Mike Brum assumes that the H stands for heading, and I assume that his assumption is right. Thanks to Mike for pointing this out.

Proxy type
Geotag can use a proxy, if you are behind a firewall. Here you can specify what type of proxy (if any) Geotag should connect to. The options are: No proxy, HTTP proxy and Socks proxy.
Proxy address (host:port)
If you specify a proxy type other than 'No proxy', you need to tell Geotag which proxy to use. Enter the proxy's hostname or IP address, followed by a colon ':' followed by the proxy's port number. Ask you resident computer expert, if you don't know what this all means.
Additional image file types with XMP
Geotag can store locations for any image file, as long an XMP file exists for it. Let's say your camera creates files named 'image.xyz'. Even if exiftool can't read from those files there might be a way creating 'image.xmp with third party software. Just tell Geotag that xyz files with XMP files are valid images files and you can geotag them. All you do is enter a comma separated or space separated list of file extensions into the settings field and you are ready to go. In our example you would enter xyz.
External programs
Browser
Browser path
Geotag tries to find a suitable browser automatically. Sometimes this is not a good choice. Here you can point Geotag at a different browser without the need to change your system's default browser.
Exiftool
Exiftool path
Geotag uses Exiftool to write location data to files and to read it from RAW and XMP sidecar files. If you select Help->What next? from the menu bar and Geotag says it can't find exiftool, here is what you do: Open the settings window. To the right of the Exiftool path field is a little button with three dots in it. When you click on it, a file chooser window opens. Use it to browse your file system and select the exiftool executable (exiftool.exe for Windows or exiftool for Linux). Afterwards, select Help->What next? again, to make sure Geotag no longer says it can't find exiftool.
Additional Exiftool arguments
This is a rather advanced configuration option. Here you can specify additional command line arguments (separated by spaces) Geotag will specify for Exiftool when running it. Use at your own risk! Here are examples of what you can do with this option:
  • -P - Leave the files original date/time unchanged when writing the location data to it.
  • -overwrite_files - Normally if you write location data to a filed called, say, image.jpg, exiftool keeps the original image renamed to image.jpg_original. This is normally a good idea, but uses twice the space on your hard disk. If you specify -overwrite_files, the original file will be replaced with the image file containing the location data. To quote the exiftool manual: Caution: This option should only be used if you already have separate backup copies of your image files.
  • "-Copyright=Joe G Geotag" - This example shows how to pass arguments containing spaces. Just surround the entire argument with quotes. If you want to pass quote characters (") to Exiftool, you can surround your argument with single quotes like this: '-Copyright="Joe G Geotag"'.
Keep backups of images when writing to files
The -overwrite_files option seems to be popular enough to have its own setting. The default is to keep backups of files. Deselect this option if you are confident that Exiftool won't mess up your files.
GPSBabel
The -overwrite_files option seems to be used often enough to have its own setting. The default is to keep backups of files when writing to them. Deselect this option if you trust Exiftool not to mess up your files.
GPSBabel path
Geotag uses GPSBabel to read GPS tracks straight from your GPS. If Geotag can't find GPSBabel (Help->What next? will tell you), you can tell Geotag where to find the program. Read 'Exiftool path' above to get the idea.
GPSBabel protocaol
Here you can specify the GPSBabel input format. It defaults to garmin for the simple reason that this is the brand of GPS I use. If GPSBabel doesn't work right out of the box for you I strongly recommend that you get it to work on the command line first and use their web site to sort out problems. When it works, this is the place where you specify the argument to the -i option.
GPSBabel device
Same as above, except this time you specify the GPSBabel argument for the -f option.
Dcraw
Dcraw path
Geotag uses Dcraw to extract images from RAW files.If you use RAW files and Help->What next? tells to you it can't find Dcraw... well, you should get the idea by now..
Google Earth
Google Earth path
This setting is only available for Linux users. If Geotag can't find the Google Earth executable, this is the place to specify it. Windows and MacOS users do not need this setting, therefore it is not available to them.
Clipboard
Monitor clipboard
Geotag can update image coordinates from the clipboard. Select the check box here to enable this feature.
Latitude first
By default, Geotag assumes that any coordinates copied to the clipboard are latitude first, longitude next. If the coordinates you try to import from the clipboard are the other way round, unselect this check box.
Letters for 'North'
Letters for 'South'
Letters for 'East'
Letters for 'West'
Here you can specify which letters are recognized for North, South, East and West when trying to read coordinates from the clipboard. See the documentation for clipboard imports to find out what you can do with these settings.
Export
Google Earth
Store thumbnails in KMZ files
When exporting image and location data to Google Earth KMZ files, Geotag can store a thumbnail of each image in the KMZ file. Select the checkbox to enable this feature.
KML image path
When exporting to Google Earth KML/KMZ files, image paths are stored as paths on your local hard disk. If you want to use the Googleearth files on a web server you can specify the path to the directory containing the images here.
KML icon URL
When exporting to Google Earth KML/KMZ files, Geotag needs to specify a marker icon to be displayed for each image on the map. The default icon is this:

To use a different marker icon, specify its URL here.
KML description header
This is now getting a bit technical. Feel free to ignore this and the next item. Power users only! A KML/KMZ file contains a description for each image contained. This description is usually displayed as HTML. Anything you enter here will be added before the description generated by Geotag. This can be pretty much any HTML including the opening tag of a <div> element. If you don't know what you are doing, this can seriously mess up the exported KML/KMZ files. Don't come running to me.
KML description header
Anything you enter here will be added after the description generated by Geotag.
Place name look up
geonames.org
Geonames URL
Normally the geonames.org service doesn't change the name of their server. Should the name of their server change, you can point Geotag at the new server by changing this setting.
Search radius
When looking up location names from geonames.org a search radius can be specified. Normally only the nearest location to the image's coordinates is retrieved. You can click on the little check box to the left the number field to enable the use of a search radius and then specify the radius (in whatever distance unit you have chosen). Several locations up to that distance from the image coordinates will be retrieved and you can choose one of them for the image. How many results are retreived is determined by the next setting:
Number of results
Do not retrieve more than this number of location names if a search radius is specified. This setting has no effect if the use of a search radius is not enabled.
Retrieve Wikipedia place names
First enable Wikipedia place name lookup by selecting the check box to the left, then specify how many location names to retrieve.
Override query language
If your local language is not known to geonames.org, it will return place names in German. This is often not the desired behaviour. First enable using a different query language by selecting the check box on the left, then specify the desired language in the text field. Enter the language as a two letter lower case identifier, e.g. fr for French or it for Italian. If you leave the field blank (or enter en), place names will be returned in English.