Also FYI there is a question on the Microsoft Forums from back in 2020 regarding the same issue we're having. Doesn't seem to be a solution though.
( https://answers.microsoft.com/en-us/outlook_com/forum/all/images-received-in-html-email-are-not-loading/d3899252-0665-49e3-af82-f78112080eb4 )
@Rachel I have posted this on Twitter as well
( https://twitter.com/kevinMario/status/1518835012493225984?s=20&t=d4WX1FYXx6vJKQUKstY5Cg )
and I can confirm that from the screenshot that Sendgrid ( the service that sends our comms ) are using http so I'm not sure if that is the problem?
Do let us know if your theory worked! :)
Experiencing the same thing, @Rachel have you figured out why this happened?
We specified the src value with an actual URL so I don't think the issue is in the actual email template itself. And when the email is opened in Outlook Desktop App it shows properly.
Only when we tried opening the very same email from Outlook Web, the images refuse to load - inspecting the DOM reveals that the original value of the img src has now been moved to originalsrc - and the src value has now been changed to data:image/gif;base64,R0lGODlhAQABAIAAAAAAAP///yH5BAEAAAEALAAAAAABAAEAAAIBTAA7 - exactly the same value that you have on yours.
The fact that we use different images and different CDNs, yet we get EXACTLY the same value for the src feels like an issue on the Outlook Web side.