If the recipient is not using Gmail.... There’s no way that Gmail is tracking any activity on the account without the user being aware and involved.
But as has been shown, clicking on an embedded link (or showing images by default) reveals information regardless of the recipient's email system.
Gmail is not doing the tracking. Streak.com is doing the tracking, and Gmail is just the platform they are using to deliver the tracking information to their clients.
If you don't want to be tracked, don't let your email client fetch the web bug images and don't allow your client to honor Return-receipt or DSN requests. If you are using Gmail as your email client, you need to disable automatic image loading and refuse any read-receipt requests (see here for a demo on that). If you are using some other email client, RTFM.