A red "X" means two things:
1) You're using Internet Explorer
2) The image cannot be loaded. This is generally not your fault but the fault of wherever the image in question is stored.
I believe that you can right-click the red X and go into Properties to see the exact URL of the image, you can try copy-and-pasting that into your address bar. That will help occasionally, when a site won't allow hot-linking of the image but will let you view it directly. You might even be able to view it directly when right-clicking, but I don't think so. I don't use Internet Explorer so I can't remember its behavior with red X's exactly off the top of my head.
Generally, though, if there is a problem like that, it's quickly noted. If you're getting a lot of them, then perhaps there's a problem on your end. A dial-up internet connection might possibly cause an issue, too; possibly there could be a timeout hit? Unlikely but possible.
Actually, try this first. Hit F5 or click the reload/refresh button in the toolbar. This will reload the page and it will try again to load the images that aren't coming up. If more appear, then it's some kind of internet connectivity problem, perhaps caused by your internet provider.