If you're browsing with Mozilla Firefox, the AdBlock extension might block images.
The red cross sign means that an image that appears couldn't be found or loaded. It might be the fault of the website owner.
Otherwise, if you're using explorer, on right click and go to "internet properties". Choose the "advanced" tab and scroll down to the section called "Multimedia". Check the box saying "Show images".
If that doesn't help, go to the page where images aren't shown and press alt+F5. This will do a forced refresh, so hopefully the images will be forced to load. This works on Windows platforms (I don't know about Mac).