You can get away without the width, height, alt text and trailing slash but they're nice to have, and watch out for accidentally posting a page-filler sized image. If the file you want to link to doesn't end in gif, jpg, jpeg, png or possibly webp it may not work. And some dumb web sites will occasionally post a jpg file but name it as png or something, which is another rake in the grass to be aware of. It usually works anyway, but it's kinda rude, and always makes me question the competence of whoever put the image up in the first place. And it's easy to get caught out in turn because one usually trusts file extensions to be correct. The concept of a file extension isn't that difficult to grasp, although MS have been valiantly trying to obfuscate it for everybody for years.
If you post a file link (.zip, .jpg, .md, anything) inside an <a href="...> you get a clickable download instead of a web page opening.
Finding the right URL for the image tends to be fiddlier these days. Right-clicking and choosing 'open image in new window', or 'copy link to image' may be needed. And some image links will will broken by the remote server if you attempt to reshare them. It was simple, once upon a time. Then techies, marketing, sales, the bean-counters - people, basically - got to it, and we ended up with the current mess.