Updated hotlink protection with new Google Image Search

[Ian Evans]

As you can see from this thread on Webmasterworld 
(http://www.webmasterworld.com/google/4537063.htm), a lot of people are 
upset about the new Google Image Search changes that allow visitors to 
see much larger previews of images without visiting the site. Google has 
also stopped showing the site in the background which removes any 
potential visits from people seeing the context of the image's "home".

I currently have use the following in my nginx.conf:

error_page 403 = /403.shtml;
expires 30d;
valid_referers none blocked *.example.com example.com ;
if ($invalid_referer) {
return  403;
}

The 403 page actually looks up the requested image in my database then 
redirects the person to the page that it's part of.

That's worked for a years but it's not working as well in the new Google 
Image Search and we're now serving up more image requests without their 
surrounding pages, and yes, the advertising that allows me to travel to 
take the shots at events. From the thread (and looking at my logs) it 
appears that Google seems to be sending the referrer less and less, 
especially in situations where people are logged into to Google.

While reading about this new search that has people up in arms I came 
across this site and how they're handling it. When you see the larger 
image preview pop up on the new Google search the image flashes for a 
second then gets replaced by the image covered by a warning and an note 
to click to see it without it:

https://www.google.com/search?q=site:fansshare.com&hl=en&safe=off&tbo=d&source=lnms&tbm=isch&sa=X&ei=SIEQUdDAPMnkygGKrYGACg&ved=0CAoQ_AUoAA&biw=1266&bih=878

Any idea how they're doing this? Any idea how to implement it with 
nginx? From what I've read elsewhere some of the new hotlink options are 
going as far as intercepting the image requests and adding overlays with 
PHP and GD to create the overlays if they're not on the host site.

Thanks for any thoughts.