I noticed a Yahoo! IP address systematically loading images from my website this morning, directly without visiting the associated pages, and went over to Yahoo! to have a look. What I found was that my images do return in search like usual, first as thumbnails and when a thumbnail is clicked on the full version appears on Yahoo!
I have both image hotlink protection in place and so I was a little surprised when the Yahoo! page did not redirect back to my site AND did not display a blank page so I checked and sure enough - the image is stolen and on Yahoo in full.
The kicker is that to get to my site from that image you have to click on a link that says "continue anyway" (not my web address or anything intuitive) which is placed right beside this message...
Loading the page might take you away from Yahoo! Image Search (Not recommended)