You need to put "[img]"%20first%20then%20the%20address%20then%20"[/img]" at the end.
If you put your "mouse/pointer" on the "Img" tab It will give you a example.
I had this problem too. THANKS BOB
Also if you hit the "Preview" tab it will show you what you post as a "post"
and if it works then you can submit.
I found that opening a post that was edited for you in one window and starting a new post in another you should be able to find what/where you are doing wrong, and using your "edited" post as a templet.
If I post a photo I always "Preview" it first just to make sure it is working right.
Hope this helps