I believe that indicates the browser could not load the image, just as IE has it's own placeholder icon.
You didn't give specifics as to exactly what images aren't loading, but if it's things like the Reply, Edit, Quote, Avatars (forum software graphics), then you may either have a network issue preventing the content from loading or have a browser issue or setting preventing the content from loading as the content is working normally. I'd first suggest clearing your browser's cache. If that doesn't work, then provide a specific example of what isn't loading. Perhaps a screen capture will help more than words.