I just noticed that Bing Image Search is hotlinking our images. That's right: the image that you see is not on Bing's servers, but on your server and using your resources even when the viewer doesn't visit your website.
When a user clicks on the image, Bing opens a new window with the full size version of the image and will NOT direct the visitor to your web page => as good as no chance that this viewer will view pages on your website.
You could try to work around this with a frame breaker but this will only work until Bing crawls your website again. After detecting the frame breaker they work around it and add the message "Displaying this page may force you to leave Bing Images. Opening the page in a new window will prevent this."
Conclusion: The value of Bing Image Search for webmasters is 0. It actually COSTS bandwidth. This makes Bing the biggest content thief ever.