I googled "fusker" and lo and behold fusker.com came up as the first result. Apparently fusker is a free script you can put on your site, sort of like a blog program, but for hotlinking images instead. There is not just 1 site running fusker, there a lots... maybe around 100 or so. So blocking one domain in htaccess probably won't solve all your problems.
Also, each site lets visitors download a toolbar if they want, so they can submit galleries they think should be fuskered, right from their browser as they find them.
Finally, I've spoken with one of the (large) sponsors who has a link on the fusker.com site, and I believe they are paying fusker.com to include their sponsor link with the script when it installs. The script is likely "free" for download since it comes with this built-in advertising. It is quite a racket they're running.
Anyway, check fusker.com for a list of the sites running this program.
