Geotag is a self-signed Java application. This just means that I'm not willing to pay a lot of money for a commercial certificate I can use to sign a free application. The latest versions of Java 7 (update 51 and later) won't allow self-signed applications by default. You will see an error message like this:

You will have to tell Java to make an exception for Geotag. You have to open the Java security settings panel and add both and to the exception site listlike this:

After you have done this, Java will still nag you about security risks, but you should be able to run Geotag. To get more detailed instructions for this procedure have a look here and here.