enigma1 - 7:20 pm on Aug 15, 2010 (gmt 0)
If they have any value for SE ranking, though
Depends how you're serving them. They can have value from various factors. For instance how the person views the external page. Does he allow 3rd party cookies? Does he have a toolbar that monitors his preferences? Is there a mechanism that reports these access to the images so it counts towards you in the search results?
Then how does your server sends the images? Does it use thumbnails or a lower res image so you conserve b/w? Is it a straight image access or it passes through a thumbnailer etc.
And if you decide to block them how do you block them? 403? 301? There is a difference. You can make them count in favor of your site.
Finally how do you detect the hot-linking? Is it referrer based or some other method? I have seen sites bringing up a broken layout because I block the referrer when I browse online. I only see one page then I am out of course.