8 – Define a default image when using the image as a base field in a custom entity

I have defined a type of custom entity with a basic image field. Now I want to have a default image that seems to be pretty tricky: when I set a default image on a field api field and export the configs, I can see that the file's id is Picture is defined. But when I create a custom entity, I do not know which file an image can have unless I just create the image file at the time of creating / updating the type of entity.

Is there an appropriate way to define a default image in the definition of the base field of a custom entity?