That would be REALLY nice!  And might prevent some mildly embarrassing mistakes - not that I would know from experience or anything like that!! pfffffft
Well, OK, maybe I would lol

What is preventing you from proofing your posts before hitting the "post message" button.

By the way, you can edit your posts for up to a couple of hours after you post them but they will be moderated for a few hours before being reissued.

For now you could preview the URL by opening is on another page and making sure it is the right photo, or checking it right after you post and then editing it if you have to.

OK, but let's say you are including a photo & you accidentally copy the wrong url, so the photo that ends up being posted is NOT the one you wanted to use. A simple preview button would be much easier than having to edit what's already posted then wait for a mod.

Having a post preview function would be nice to have.

Peace...