When too many users use adblock, you're going to have a situation like this:
http://www.kbb.com/ Where every site you visit says you can only access the content if you turn off adblocker.
Dilbert: For a time there, both the comic images and the ads were being served right from assets.amuniversal.com/, and used what looked to be a long hexadecimal ID for each image.
Checking it now, that doesn't seem to be the case. Huh.
Something like that, with a long hashed value for each image, and not placed in an outwardly-visible subfolder, would seem impossible to block.
Randall Munroe did something like that for one long-running comic, #1190: Time.
It updated every hour. To prevent spoilers, he encrypted the filenames. This is the final image's filename:
4b9222127fb1e3fdc81781fb67a465f3ee10189881aa4572932dd3a44cb81920.png
If that's all the page tries to load for ads or content, with the server figuring it all out behind-the-scenes, blocking might be fairly difficult, and adblocking users might be forced back into the hell of sluggish processor-intensive ads and malware served off of a Pentium 133 on a 128kbps ISDN connection.