Btw I am using https://bruzu.com for og images on few of my websites.
I tried using author image and it looks ok here: https://og-image.wzulfikar.com/**Hello**%20World!.png?theme=...
For images, you can use a url that starts with http/https or use a short syntax like svg/twitter (will fetch twitter logo from svgporn), unavatar/acme (will fetch "acme" profile from unavatar.vercel.app), etc.
I tried using author image and it looks ok here: https://og-image.wzulfikar.com/**Hello**%20World!.png?theme=...
For images, you can use a url that starts with http/https or use a short syntax like svg/twitter (will fetch twitter logo from svgporn), unavatar/acme (will fetch "acme" profile from unavatar.vercel.app), etc.