Define /local path

When I applied an image to a card header using the default ‘balloons-header.png’ image, the image was pulled from a web address and appeared correctly on the card. Now I am attempting to use ‘local’ images, i.e. images located in the container HA installation. I have placed images in the HA/config/image folder, including the ‘balloons-header.png’ image. Using the suggested path /local/‘filnam’ does not access the image nor does /local/image/‘filnam’. I assume that the /local path is internally defined within HA but that definition is not apparent.

You need to create a folder called www in the config folder and put your images there. /local/filename maps onto this.

And you need to restart home assistant after creating the www folder.

WWW folder already exists. That folder contains all of the ‘custom’ elements, like lovelace custom cards. That seems a strange place to host images, particularly when there is an image folder. It does work, however, at least for the ‘balloons-header.png’ image.
Are there particular image format/size requirements for images used for headers/footers? Other images placed in the WWW folder do not seem to work.