Done this way on media items and regular attachments.
Knowing whether a remote link is an image would require server work. For instance, many people will just post a link to the remote page with the image and ads. If you're embedding the image directly into a post, then maybe you don't want it to be clickable. Or maybe you're embedding the thumbnail, in which case the clickable link might lead to the page with ads.
In other words, this doesn't seem like a reliable (and thus plausible) solution.
Yes I've thought about it before.
Posted: April 6th, 2014, 03:42 PM
This could be done through a plugin, though... Eg add a 'zoom', zoomedia or lightbox bbcode that will automatically act as a URL bbcode, but load the target in zoomedia.