There are some blocking apps for Chrome: https://chrome.google.com/webstore/detail/ugly-email/ldgiafa... https://chrome.google.com/webstore/detail/pixelblock/jmpmfcj...

They're based on a blacklist so they don't catch all tracking pixels. And then most emails contain images I want to see and that have tracking ID's attached anyway, which is a problem that can't be solved with a blocker.