Preventing hot-linking generally works by examining the referrer field on the incoming web requests, and if the request is coming from an external domain, the request is prohibited.
If a visitor is using a browser that doesn’t send a referrer field to the server, they won’t be able to see your images, even if they’re browsing your site. Since some browsers allow the user to turn off the referrer capability, I generally don’t think the prevention of hot linking is worth the trouble it causes.
I expect if Classics encountered this issue, he may have that turned off in his browser? Classics?