NGINX - Can't set content-type header
The /etc/nginx/mime.types file already contains a mapping for URIs ending with .img, which is set to application/octet-stream.
When you edit the file, did must also remove this existing mapping.
Alternatively, you can override the content-type for a single URI.
For example:
root /path/to/root;...location = /images/logo.img { types {} default_type image/svg+xml;}