If you posted the image link, then the image appears to be embedded into your post, but it's not on the TBD server itself. If the image is updated at the source, then the new image appears in the post automatically, since the TBD server goes to the source every time this post is opened.
On the other hand, if you copy-and-paste the image itself, then the copy appears on the TBD server and would not automatically update if the original changed.