Have the server inspect each request for an image and look at the referrer: http://en.wikipedia.org/wiki/HTTP_referrer If it's anything from assemblergames.com, let it pass, if it isn't, deny (or redirect to an alternate image, like goatse, until they've learned their lesson). If it isn't there at all, it's up to you. I've supressed all referrer headers in my browsers by default, only enabling them when necessary. Most sites that check referrers opt for simply not delivering anything, a handful send an "missing or invalid referrer" replacement image.
Just google for "how to detect hotlinking". Here's one example: http://www.tamingthebeast.net/articles6/hotlinking-protection.htm
Once a forum I went on had this exact problem so they set hotlinking disabler to a SWF that made a really high pitched sound. Needless to say the leeching stopped fairly fast.
I love it when someone posts in a forum a hotlinked image, and it comes through as gay porn, or something crazy. Please do this, then screenshot so we can all laugh at them.
I remember hotlinking from somethingawful.com years ago putting their funny pictures online, only for them to later switch them to overtly pornographic images lol.
depending on what it's costing you, don't those count as inbound links that help your search engine placement? Is it on a website of relevant content?
