It seems that there's no way to upload an image from command line or to make a post to instagram from command line
Looking at the API docs here https://developers.facebook.com/docs/instagram-api/reference/media under the "creating" section it explicitly says that "This operation is not supported".
Instagram never offered an API for publishing, they always wanted you to use their App for sharing, with all the included features (filters and stuff).
So there answer is no, there is no API for it.