Interestingly, adblockers should be careful about doing stuff like this, as lots of sites would love a check as simple as "make a request to /twitter-sponsered-ad-paid and deny access if it fails"
<img src="/an_existing_image.jpg?&ad_box_" onerror="alert('You are using adblock')">
1. Look into the most popular filter's used by adblock extensions: https://easylist-downloads.adblockplus.org/easylist.txt
2. Choose for example a querystring rule from the beginning (from the "General advert blocking filters")
3. Append it to the url of an existing image
4. Use the onerror event to detect if it wasn't loaded
Since it's like playing whack-a-mole, I think most ad blockers simply don't care if their presence is known.
If adblocking is all about user choice then it's only fair that sites have choice to serve that content too. Right now it's incredibly hard for sites to reliably know if someone is using adblock.
Attempting to purposefully disguise that usage goes beyond any accepted ethics of using adblock today.
no that's not true - it's "easy", as long as you have cooperation from the advertising network. Their ads could do some callback onto the main page.
There are also constant updates to counter this. If you check the adblock forums, there are dozens of threads every day about how to get around checks on sites and even disable messages that specifically show up to adblock users.