I use firefox, I also tried on brave and have the same issue, signed in or not.
I just investigated a little bit, and lemmy.world's requests to the images returns 500 (with a 404 inside):
https://lemmy.world/pictrs/image/b8ed3feb-e396-4c22-b6f7-a170ed871fc1.png?format=webp&thumbnail=256
However it seems to be an issue with the "format" and "thumbnail" parameters, as just the image link works:
https://lemmy.world/pictrs/image/b8ed3feb-e396-4c22-b6f7-a170ed871fc1.png
🤷♂️
no common sense allowed in this thread, sir. only AI hate bandwagon please.