I'm wondering if I posted a link to an image as a Newbie, and then become a Jr. Member, will it magically turn into a visible image once I reach the rank, or will I need to go in and edit the image? (Sorry to get so esoteric!)
No, your post stays the same and the forum engine just renders it differently depending on your status. If you're a newbie, it will render your post just as a text array, if you're junior (or copper), the engine will scrape your images and render them.
This happens when a page loads, not when you post your reply.
Hope thatll make this clearer.