The first example isnāt a link to an image, itās a link to a website. The website happens to be a Wikimedia Commons image description page, but that fact doesnāt affect change how Discourse displays the link, and the text is (I believe) controlled through the metadata provided by the website that is being linked.
It is actually possible to include images in a post without first having to download and re-upload it, but to do so, you need to paste a link to the image itself, not a site containing that image. In the case of a Wikimedia Commons image, you can get to the image itself by clicking on the down-scaled version contained in the description page.
For example, inserting the link
https://upload.wikimedia.org/wikipedia/commons/a/a6/ISS063-E-38446_-_View_of_Earth.jpg
produces:
As an aside, please check licenses before including images in a post. Your example image is published under a license which requires attribution to the creator of the image.