Recently, I noticed that a significant percentage of my web site traffic was for a single image 
of Blobby the Blue Lobster, all with referrer strings indicating a particular web board. Sure enough, I went there and found that one functional illiterate was using this picture as his avatar in his conversations with a bunch of other functional illiterates.
If you don’t believe me about the functional illiteracy, here is word for word one of his posts to that forum:
OMFG that was so fucking funny i cant belive that people belive that shit haah…john malm wow im so happy hes gone again after reading this.
But i msut say between reading all of that and the XMF interview the romm is freaking spinning ive read alot today including a bunch of video games ahah well tt you all alter
Anyway, I don’t like picture leeches much, and I especially don’t like illiterate ones. So I put the following in my /etc/http/conf/http.conf:
RewriteEngine On
RewriteCond %{HTTP_REFERER} ^http://www.echoingthesound.org/.*$ [NC]
RewriteRule .*blobby.*\.jpg http://xcski.com/~ptomblin/pork.gif [R,L]
Which directed every request for his avatar to 
a much smaller picture. But he didn't get the message, even after I wrote to him telling him he should check his avatar. So I took more drastic measures, and yesterday I changed the redirect to 
an even smaller picture that makes it more explicit.
Today I see on that web board a post from him saying
Ok so i look at my avatar and some guy must have hacked it and it said "I'm a PIcture LEech I suck" and someone ahd contacked me before adn tlaked somethign about my icon that i needed ot refresh it or somethign but it made no sence to me so whats up?>
Amazingly enough, he's changed his avatar, but he's still leeching - the image he's using is on somebody else's site.
It’s not malice, but ignorance. Explaining bandwidth bills to these people is like expecting an 8 year old girl to be able to pass Microsoft’s MCP program. Oh ok, bad example.
An entry in robots.txt to banish Google Imagebot is probably all that’s required. I chose to move all my photos to flickr instead though, so now it’s their problem.
I don’t mind people looking at my pictures. I don’t even mind if they copy the mundane ones elsewhere, although I’d prefer it if they asked permssion and gave credit. But I’m a realist to know that isn’t going to happen every time.
I’ve found that rewriting image leechers’ stuff to some sort of Hitlery image gets them to change it quick (although on the right kind of forum they get banned before they can change it).
The best one yet was when a Xanga user used a big White Stripes wallpaper image of mine as his Xanga journal’s background image. I replaced it with a big swastika that matched his color scheme, so it looked completely intentional. The old image was in his browser cache. Within a few days I went back to find a dozen comments from his friends asking him WTF he was thinking, and a dozen replies from him going “ha ha, funny, stop pulling my leg”. A few days after that he clued in.
Like Barry says, there’s no malice, only ignorance. Lots of ignorance.
This person probably has no idea that the image they’re using isn’t somehow automagically placed on their C: drive (statistics, not a desire to slander, dictate they’re a Windows user) when they cut and paste the image’s address, and that the Internet obtains it from there. After all, it’s clear he thinks someone has hacked HIS image.
If you tell them that they’re grabbing the image off your server, they’ll either: (a) not believe you, (b) comprehend and be embarrassed, (c) fail to comprehend and (i) be even more embarrassed because they’ll think they’ve accidentally “hacked” you, or (ii) imagine they’ve become 1337.
I’d just rewrite to a 1×1 transparent GIF and watch the fun as he tries to figure out why his avatar isn’t working. Easier than trying to explain, but not too unkind.
Well, I’m not as nice as you, Steve. I liked the idea somebody else had before of making a 5000×5000 transparent gif. It would be really small (because of the LWZ compression) but would expand in their browser, and possibly crash it.
Oh, I like the 25 megapixel idea.
In the past, I’ve tailored the referral image to suit the crime. Freepers get a special image with included text about stealing private property. Homophobes get explicit gay porn – ESPECIALLY if they’re posting on a family-friendly site. Reactionaries have gotten Hitler, Michael Moore, one of the fine family of goatse-related graphics, or My Pretty Pony, depending on my mood.
If I could figure out a way to include a “lessthan”/DIV”greaterthan” code in a graphics file so that the host would get seriously annoyed at the offender for screwing up the rendering of every page the offender posted on, I’d be thrilled. But that big gif will have to do for now.
I know you’re not as nice as me, Paul, but just using Irfanview I made a 5000×5000 transparent image and it looks like PNG might be a better choice than GIF. The file was smaller (3KB vs 20KB) and the client rendering probably has a higher overhead.
With proper tools you can doubtless craft a smaller GIF, so don’t mind me.
Why waste time on these people one at a time, when you can stop them all simply by redirecting all requests without the proper referer?
Personally I redirect (gif|png|jpg|css|txt|mp3|aac|swf|mov|mpg|mpeg) to a page, which uses some simple SSI to show the contents “inside” the page.
This way people can view it all locally, and they can link to it, but they can’t include anything directly on their pages (not without knowing enough to not even try to do it).
So, like, I stole your leech picture to use on a few of my own leeches.
Guess that makes me some sort of a leech.