A little bit JavaScript, and a little bit CSS, Link Thumbnail shows users that are about to leave your site exactly where they're going.
When that mouse pointer hovers over a link pointing to somewhere outside of your site, the script displays a small image of the destination page.
It's a nice visual cue that serves a very real purpose: providing a clearer picture (no pun intended) of what's ahead.
Based on a javascript from arc90 lab Website Thumbs are provides by websnapr.com, thumbnails.alexa.com and msnsearch.srv.girafa.com

[05/21]
If you have problems with "thumbnail in queue" or "forbidden" text, try to use the MSN version. MSN replace Websnapr to generate the thumbnail of the website.

[5/23]
A error has been reported :
" Nice idea, but on several (not all) of my pages, the following error occurs:
truc
Fatal error: Call to a member function on a non-object in /mnt/w0202/d09/s16/b02a1f92/www/burdo.net/joomla/mambots/content/bot_linkthumb.php on line 42"
if you used the original version : erase lines 42 and 41. or replace with a new download. I've corrected this error of carelessness: I had forgotten 2 lines of check code. Sorry.