copy image from object to object

hello, i need help

assume you would like to copy the picture e. g. [id]large from a entity "campaign" to another entity "group"


i know how i make the files [id], [id]large, [id]medium, [id]small, [id]tiny . . . e. g. when i upload a picture

but i have no idea how i can do that with an existing entity-picture

nice greetings from cologne
lisha