Many brands and retailers are still sending emails with images that are loading through HTTP. However, the next Google Chrome update (Chrome 81) will cause emails with images loaded over HTTP (vs HTTPS) to no longer show up in some webmail providers. This will mainly affect Outlook.com and Xfinity’s webmail service, as Gmail and Yahoo! Mail use proxies that “auto-upgrade” HTTP images to HTTPS.
The reason Google is doing this comes down to security as mixing HTTPS (secure) and HTTP (non-secure) content can compromise privacy and security without a user knowing.
This article on ProofJump covers what you need to know about this change, as well as a HTTP Image Checker tool to help determine if you have HTTP images in your email and check if there are HTTPS alternatives.