As of late September 2020, Google Chrome (version 86) has made a security improvement and now blocks mixed content. This means if you have an image which is hosted via HTTP, it won't load in an HTTPS page. Taxi for Email is hosted via HTTPS, so it's important to use HTTPS for your images.
If you upload images to Taxi you will not be affected as mentioned above Taxi for Email is hosted via HTTPS.
If you are using your own hosting:
Change your image to be prefixed with HTTPS:
Depending on your image hosting supporting this you can edit the image URL changing it from HTTP to HTTPS. You will need to update the image links in your Email Design System to use https. The image servers will need to be set up correctly before you can update the URLs to https. Once this is updated all the images in your Email Design System will display correctly as they are now HTTPS
Use Taxi CDN:
You can change your images to be hosted by the Taxi CDN. The Taxi CDN has been using HTTPS by default since earlier this year.
To host your images via the Taxi CDN
When adding an image to a module, select 'Browse'
Click 'Export Mailing'
Select where you want to export the mailing to
This will add links into your Email Design System to the Taxi CDN. All images belonging to the Email Design System will also be hosted by the CDN. Find out more about the Taxi CDN here