Ask HN: How to block marketing trackers in Gmail

In the good old days (before 2013), Gmail would not load external images unless you clicked the "load images" link. This way, tracking images from marketing emails like MailChimp and others would not be able to track you. Now with Gmail now caching the images, the marketers somehow have that data again (including if I opened the email, and how many times ... maybe more?). Is there any way to go back to blocking this?

(see here for more background http://www.nytimes.com/2014/12/25/technology/personaltech/ways-to-avoid-email-tracking.html)