Would it be possible to add a theme setting, which allows uploading images? Let’s say that I have a theme, which adds a background image. If I want to let the site admin to choose a custom image, I can only provide a string field for the url, but the image itself must be uploaded somewhere else. It would be nice if you could choose an image that is stored in the site uploads, the url retrievable by the setting variable. This feature is already implemented in the site settings for logos and icons.
Have you seen Include images and fonts in themes and components
I am aware of that tutorial. I should probably clarify, that in my example the end user would be the one to add the image, not the theme developer. In such a case a single setting for uploading images would be better. Furthermore, one cannot locally add images as assets for remote themes, because updates will clear them out.