You can not upload any images to AFF at all. They don't have the capacity to allow that. You can, however, use sites like Wordpress or Imgur or Photobucket to host your images for you and them embed them into your posts. To do that, in your post or story editor, click on the icon that looks like an image (top row, first icon of the fifth set) and paste the URL of the image in there. Your image will be inserted wherever your cursor has been placed.