Ok so we know how to embed an image via directly uploading into a post, but how about embedding an image stored elsewhere via its address?
There is an 'Insert Image' icon on the editor toolbar (mountain landscape icon), there you can enter an external link, but the result is not clickable so the embedded image is all you get. I'll use it here (this is embedded via it's address not via upload into the post) -
What we want to see is the externally stored image embedded here and for it to be clickable - for it to open the full image.
Replace ADDRESS below (twice) with the address to your image - the address should end with .jpg or .png
[url=ADDRESS][img]ADDRESS[/img][/url]
So I'll do that with the same image as above which is in fact stored 'internally' on this site's server. This might seem weird and not the subject of this post (external images) but it means I can share the image again here (and you can see all of it's 28MP), without uploading it again. This is the actual address -
It could just as well be an external site's address, which will then open that site to view the image. It can also be a dropbox link to an image.
Now I insert that address into the above code, twice; this is the result, the image is clickable the vers above isn't :
