to explain, a normal link to an image would be
www.mysite.com/images.pc.jpg for example. The link that micovwar posted was a link to a php page
http://mig2.lathwood.co.uk/r.php?d=s&f=sn41_gaffix.jpg
That link goes to a page called r.php. Everything after the question mark is a set of parameters which tells the page r.php to go away and find the image sn41_gaffix.jpg and then display it on the page. The most obvious reason for displaying graphics in this way would be to prevent people linking directly to the image for display on a forum. Effectively the link on the forum just points to r.php which is not a valid image and a red x is therefore displayed
hope that helps