fpdf.load_resource(reason: string, filename: string)
This method is used to load external resources, such as images. It is
automatically called when resource added to document by image. The
implementation in library sre try to load resource from local file system or
from network if filename starts with
https://. This method can
be overrided within subclass if you want a specific processing.
Returns file-like object.
filename or URL.