Most email clients don't fetch remote resources like images embedded in emails unless you specifically ask them to. If you're seeing pictures in your emails without having to tap something extra after opening the email, you likely need to change your settings.

As someone else pointed out, FairEmail for android additionally blocks tracking pixels even if you want to load other images.

Loading other images or resources can still track you. For example, rather than using a tracking pixel, a company could create (let's be honest, generate 🙄) a unique image for each email campaign they do, and make that a visually important part of the email, such as a title banner, and then track who loads that to see who opened the email. They could even add tracking metadata to the URL like https://example.com/email-resources/october-newsletter-header.jpg?user=your-email%40your-domain.com