I’m not a lemmy dev, I just took a look at their repository
I believe it’s the regex that detects if something is an image
A reddit image URL is :
https://i.redd.it/2obhjz2wb37b1.jpg
or
https://preview.redd.it/7s1p7mal707b1.jpg?width=640&crop=smart&auto=webp&v=enabled&s=f741210c6c54fed7c3ed06aaabdb1f0a49fd46cb
in both cases it has “.jpg” (with the dot) in it so it passes the regex. It does not need to finish with it.
Whereas the image your provided does not have that in it.
You can instead download the image and post it like this, or similarly take a screenshot.
I believe that sort of website does this on purpose to make sure they don’t waste server resources on other website that do not drive any ad revenue to them.
(if you’re not a dev, I assume this is your face right now, sorry about this: