What web server are you hosting the image on? If it is a free host, most likeily the problem is .htaccess, which wont allow off off linking: stealing other people's bandwith,(similar to what you folks do with photobucket, but they let yah)
The reason the space for the image is there is because the HTML states that theres an image of size X that should be there, if the browser gets a problem, it will just show an outline.
Take this for example:

The image is hosted on anzwers, if you haven't visited the page, you probably wont see anything. Now goto the main LU page, then come back here and refresh. The image
should appear.