How to copy one object from one model to another model with Rails ActiveStorage
You can attach the source blob to the target:
image.file.attach best_photo.file.blob
OK, I got it. I used service_url:
image.file.attach(io: open(best_photo.file_variant("large").service_url), filename: best_photo.file.blob.filename, content_type: best_photo.file.blob.content_type)