[anewone]

Tracking pixels are the closest we have to determining whether somebody opens (& hopefully reads) the email. Click rate is the next best thing but unless you are an incredible marketer it will be far below open rate, possibly 1/4 or less. What Google is implying there is to use tracking images and automatically unsubscribe users that don't load them after several messages.

[mcv]

Google is not explicitly saying to use tracking images. That might be the only possible implementation of this advice, but they're not explicitly telling you to do this. Also, consider their use of the word "consider". It's not a hard rule to them.

And personally, I still think it's a bad idea to automatically unsubscribe people who are interested in your newsletter merely because they're not loading images. At the very least, make it very explicit that you're going to do this, and maybe give them the option to turn the auto-unsubscribe off.