Stoxnet forum members often attach photos to their messages. All other forum members are able to see these pictures - they appear beneath the message as the author - for example in the topic "John Riley's New Car - Exclusive Photos", forum member Colin C recently posted some photos:

When you are not signed in to the forum, you can't see these photos. Instead, they show as links to downloadable files, like this:

If you click on the links, you'll be able to view them once you sign in. If you are not a member, or you are a new member who has not yet completed all four steps of the registration procedure, you will see an error message as shown below:

In order to be able to see photos attached to forum messages, and avoid the error message as shown above, you must be a registered member of the forum. You can register for free via the Register link, and you can read more about the registration process here.