In order to post external links, you need to have written 10 posts, like John said. After 100 posts, you can add a signature to show up in your forum threads
That is odd that it would say they are not approved. The image needs to be either in JPG or PNG format and have a maximum size is 10 MB. You can also drag and drop image files into the forum. I would suggest signing out and back in again.
Lastly, a few weeks ago, we launched the new forum, which you are using right now. We are in the process of updating the forum, but this could take some time for our web developers to implement. Trust me, the new forum is a lot cleaner looking than before, though it may lack some features. In our forum, we have a thread for feedback to the forum, you can contribute there if you see anyhting that you believe needs changes. Of course, our team has a set timeline for things to get done, but user feedback is important to us.
Let me know if you have anymore questions!