These exist because <i>Internet email was never properly designed in the first place</i>(!) -- initially, a long time ago, there was no way to know if a recipient opened your Internet (SMTP/POP3) email (compare this to a Bloomberg terminal or Microsoft Outlook, where emails to other users of the same email system would return a return receipt automatically in the case of Bloomberg, and if requested by the sender, in the case of Outlook...)<p>But the tracking pixels, aka, "spy pixels" -- are there to get around this earlier limitation...<p>The way it works: A link to an image, an image hosted somewhere else on the Internet, is placed in an email. Well, now the email system needs to display that image, so when the message is opened, the URL for the image is opened, and if that's a unique URL -- then it can be tied to a specific piece of email -- in effect letting the party on the other end know that you opened the email, when your email client went out to the Internet to fetch the graphics for the image...<p>Is that good or bad?<p>Well, it depends on one's point of view...<p>Certainly it's bad for privacy... but what about transactions in business where one party needs to know that the other party received something important?<p>You could compare this to asking UPS or the Post Office to put package tracking on a package, which is a very beneficial service to businesses, because it lets them know that a package they have sent is now in the customer's hands, and their responsibility (at least as far as shipping and getting it into their customer hands) is now over...<p>Certainly you would want to know if an intended recipient actually received Bitcoin, or other digital currency you sent, as part of an online transaction you were involved in...<p>Also, by reciprocity, if you wanted that, then by reciprocity you should also be OK with other senders/counterparties in digital currency transactions with you -- being able to know with certainty if you had received the Bitcoin or other digital currency that they had sent...<p>It's almost the same thing...<p>People should not blame the Internet for inventing this "creative work around" for tracking -- for the Internet's earlier invention of email which didn't know if anyone received an email or not...<p>A well-designed future email system -- permits message tracking as an option -- but doesn't force it down users' throats without consent.<p>Also, a well-designed future email system -- would permit a high degree of granularity on what the end user wants to allow others to track and what they don't...<p>For example, they might set the system so that their friends and family (or other whitelist of names) could receive automatic confirmation when their messages are received, opened, etc. -- but this wouldn't happen for unknown/unsolicited senders...<p>But anyway, that's "why" of the "spy"...<p>...pixel, that is... <g>