Image Server not working on Gentoo Linux (CORS policy)

[monyarm]

I'm running Gentoo Linux, and the Obsidian AppImage.
I had to change firewall settings to get the image server working. Now it works if I open the URL in my browser, but in Obsidian, I get no image, and the following console output:

Access to image at 'http://localhost:3837/Fire_Force_English_Logo.png' from origin 'app://obsidian.md' has been blocked by CORS policy: No 'Access-Control-Allow-Origin' header is present on the requested resource.
Fire_Force_English_Logo.png:1

GET http://localhost:3837/Fire_Force_English_Logo.png net::ERR_FAILED 404