Invisible image on page? How is this done?

K, so I've been dabbling with an adult site and I'm trying to get some pics indexed in g00gle. While checking out the competition, I've noticed that a lot of them appear to be redirecting to their sponsor when you click to see the page the image is from. Thing is, after checking where g00gle says the image is from, it appears that g00gle actually thinks the image is on the final destination page... (eg there is no redirection happening) but xxx.jpg does not appear on the page source. Additionally it is not a case of iframing either.

Any ideas on how this is done?

It's the same method as trying to prevent someone from hotlinking your image would use. (I believe.)

So when Google indexes your page,
case 1.
it follows through from the referring URL to the image
case 2.
The website allows hotlinking and direct browsing from the robot GOOGLEBOT to crawl.

Hope that helped.

Not sure if that helped

Case 1.
There is no link for G to follow (that I can find "on page") maybe its linked with java script?

Case 2.
not sure if this matters because the image is not on the actual page.

additionally if you try to load the image up directly in the browser (eg 3w.pornsite.c0m/xxx.jpg) it brings up the same sponsor page... but in the address bar it says 3w.pornsite.c0m/xxx.jpg

maybe I'm just too confused to make much sense of what I'm asking lol

My bad, I missed the nonredirecting part. But some fancy htaccess + robots.txt can solve that.

if it's your own webpage and you can reference a stylesheet you can set an image property of display: none;

edit: sorry, this has nothing to do with your post, i just read the whole thing now