To win this fight, you need to convince users (and not just the techies on HN) to care. You aren't going to convince site operators to hamstring themselves over an issue their users don't care about. (Even if you do, unless you win over ever single site, all you will do is kill the ethical operators and leave the unethical one standing, let like antibiotic resistant bacteria. Is that really what you want? )
I think it would be pathetically easy to convince them to care, are you kidding? The problem is notifying them that it exists. Despite what many seem to think, people do care about their privacy and most people would find this extremely creepy. If your gmail alerted you that images could be used for this purpose then much more users would care. The problem is that users have no idea that this can occur and it is not fair to them in the least.
This isn't about websites, it's about email. Ethical operators do not insert tracking bugs into email, and they definitely don't do it in a way that tries to deliberately get around long-standing restrictions in virtually all email clients explicitly designed to impede this.
