The media manager shows a preview of your image. If you use the browser's functions to download the preview, it's the preview of the image the browser will download. If you want to download the actual uncropped image at its true size you have to open the image with the media manager and then use the media manager's function to download the complete image.
BTW, I have explained step by step how to do links here in the forum. Image links are made exactly the same way except for the leading exclamation mark (!).
To be sure, this forum uses another syntax for formatting as DokuWiki. The forum is not run on DokuWiki but on Flarum, which is another software product.