(In reply to Valentin Gosu [:valentin] (he/him) from comment #2)
The image also doesn't load with Chrome without DoH. (please let me know if that's not the case for you)
It sounds like this might be a webcompat issue, and if we were to fix it, we should make sure to do that in a manner that works the same across all browsers.
MS Edge/Chrome do not display the image, but show a "broken image" icon next to the Alt Text so it is slightly more obvious what is going on. Their consoles indicate:
Mixed Content: The page at 'https://archive.wvculture.org/vrr/va_view.aspx?Id=1588309&Type=Death' was loaded over HTTPS, but requested an insecure element 'http://images.wvculture.org/1953911/0002943.gif'. This request was automatically upgraded to HTTPS, For more information see https://blog.chromium.org/2019/10/no-more-mixed-messages-about-https.html
And then the 404.
I don't see any UI informing the user why the insecure display content didn't load in Edge/Chrome. Their lengthy site permissions panel has the option to allow insecure content, but it would be pure guesswork on a user's part to go change that setting when an image is missing (assuming they don't use the developer tools). Hopefully we can do a bit better.