[davidw]

Usually you might see that in Internet explorer (firefox will omit the box with red x) - and that is an image placeholder suggesting an image should be there but is not present in the location assigned. What you need to do is right click on that and choose properties and ensure an image is located in the location where that box suggests one should be or change the location of the image to the correct location. Also, if the image is present in the /path/to/your/image/ then ensure that there are no _ (underscores) in the navigation (either by means of your link or your image properties).